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Environmental Protection 
Agency 


Arsenic Treatment Technology 
Evaluation Handbook 
for Small Systems 













Office of Water (4606M) 
EPA 816-R-03-014 
July 2003 

www.epa.gov/safewater 


Printed on Recycled Paper 


Executive Summary 


•A^/>3 

on 




In January 2001, the U.S. Environmental Protection Agency (USEPA) published a final Arsenic 
Rule in the Federal Register. This rule established a revised maximum contaminant level (MCL) 
for arsenic at 0.010 mg/L. All community and non-transient, non-community (NTNC) water sys¬ 
tems, regardless of size, will be required to achieve compliance with this rule by January 2006. 

This technical handbook is intended to help small drinking water systems make treatment decisions 
to comply with the revised arsenic rule. A “small” system is defined as a system serving 10,000 or 
fewer people. Average water demand for these size systems is normally less than 1.4 million 
gallons per day (MGD). 

Provided below is a checklist of activities that should normally take place in order to comply with 
the new Arsenic Rule. Many of the items on this checklist refer to a section in this handbook that 
may help in completing the activities. 


Arsenic Mitigation Checklist 

1. Monitor arsenic concentration at each entry point to the distribution system (see Section 1.3.2). 

2. Determine compliance status. This may require quarterly monitoring. See Section 1.3.2 for 
details on Arsenic Rule compliance. 

3. Determine if a non-treatment mitigation strategy such as source abandonment or blending can 
be implemented. See Sections 2.1.1 through 2.1.3 for more detail and Decision Tree 1, Non- 
Treatment Alternatives. 


4. Measure water quality parameters. See Section 3.1.1 for more detail on water quality param¬ 
eters that are used in selecting a treatment method. 


• Arsenic, Total 

• Arsenate [As(V)] 

• Arsenite [As(III)] 

• Chloride 

• Fluoride 

• Iron 

• Manganese 

• Nitrate 


Nitrite 

Orthophosphate 
pH 
Silica 

Sulfate ^ ft> 

Total Dissolved Solids (TDS) 
Total Organic Carbon (TOC) 


° F COf ’Gf ( 

SEf 1 7.2003 


C Q 



5. Determine the treatment evaluation criteria. See Section 3.1.2 for more detail on parameters 
that are used in selecting a treatment method. 


• Existing Treatment Processes 

• Target Finished Water Arsenic Concentration 


i 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 







• Technically Based Local Limits (TBLLs) for Arsenic and TDS 

• Domestic Waste Discharge Method 

• Land Availability 

• Labor Commitment 

• Acceptable Percent Water Loss 

• Maximum Source Flowrate 

• Average Source Flowrate 

• State or primacy agency requirements that are more stringent than those of the USEPA. 

6. Select a mitigation strategy using the decision trees provided in Section 3.2. These trees lead to 
the following mitigation strategies. 

• Non-Treatment & Treatment Minimization Strategies 
O Source Abandonment 

O Seasonal Use 

O Blending Before Entry to Distribution System 
O Sidestream Treatment 

• Enhance Existing Treatment Processes 
O Enhanced Coagulation/Filtration 
O Enhanced Lime Softening 

O Iron/Manganese Filtration 

• Treatment (Full Stream or Sidestream) 

O Ion Exchange 

O Activated Alumina 
O Iron Based Sorbents 

O Coagulation-Assisted Microfiltration (CMF) 

O Coagulation-Assisted Direct Filtration (CADF) 

O Oxidation/Filtration 

• Point-of-Use Treatment Program 
O Activated Alumina 

O Iron Based Sorbent 
O Reverse Osmosis 

7. Estimate planning-level capital and operations and maintenance (O&M) costs for the mitiga¬ 
tion strategy using the costs curves provided in Section 4. Include costs for arsenic removal and 
waste handling. If this planning level cost is not within a range that is financially possible, 
consider using different preferences in the decision trees. 

8. Evaluate design considerations for the mitigation strategy. See Section 2.5 for enhancing exist¬ 
ing treatment processes and Sections 6 through 8 for the design of new treatment processes. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


u 



9. Pilot the mitigation strategy. Although not explicitly discussed in this Handbook, piloting the 
mitigation strategy is a normal procedure to optimize treatment variables and avoid implement¬ 
ing a strategy that will not work for unforeseen reasons. For many small systems, piloting may 
be performed by the vendor and result in a guarantee from the vendor that the system will 
perform. 

10. Develop a construction-level cost estimate and plan. 

11. Implement the mitigation strategy. 

12. Monitor arsenic concentration at each entry point to the distribution system to ensure that the 
arsenic levels are now in compliance with the Arsenic Rule - assumes centralized treatment 
approach, not point-of-use treatment. 


Table ES-1 provides a summary of information about the different alternatives for arsenic mitigation 
found in this Handbook. Please note that systems are not limited to using these technologies. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


in 



Table ES-1. Arsenic Treatment Technologies Summary Comparison. 

(1 of 2) 


Factors 

Sorption Processes 

Membrane 

Processes 

Ion Exchange 

Activated Alumina A 

Iron Based 
Sorbents 

Reverse 

Osmosis 

IX 

AA 

IBS 

RO 

USEPA BAT B 

Yes 

Yes 

No c 

Yes 

USEPA SSCT B 

Yes 

Yes 

No c 

Yes 

System Size B D 

25-10,000 

25-10,000 

25-10,000 

501-10,000 

SSCT for POU 0 

No 

Yes 

No c 

Yes 

POU System Size BD 

- 

25-10,000 

25-10,000 

25 -10,000 

Removal Efficiency 

95% E 

95% E 

up to 98% E 

> 95% E 

Total Water Loss 

1-2% 

1-2% 

1- 2% 

15-75% 

Pre-Oxidation Required F 

Yes 

Yes 

Yes 0 

Likely H 

Optimal Water 

Quality Conditions 

pH 6.5 - 9 E 

< 5 mgL N0 3 ‘ 1 

< 50 mgL S0 4 2 ' 1 

< 500 mgB TDS K 

< 0.3 NTU Turbidity 

pH 5.5-6 1 
pH 6 - 8.3 L 
< 250 mg/L Cl 1 
< 2 mgL F" 1 

< 360 mg/L S0 4 2 ' K 

< 30 mgL Silica M 

< 0.5 mgL Fe +3 1 

< 0.05 mgL Mn +2 1 

< 1,000 mgL TDS K 

< 4 mgL TOC K 

< 0.3 NTU Turbidity 

pH 6 - 8.5 
< 1 mgL P0 4 ' 3 N 
< 0.3 NTU Turbidity 

No Particulates 

Operator Skill Required 

High 

Low A 

Low 

Medium 

Waste Generated 

Spent Resin, Spent Brine, 
Backwash Water 

Spent Media, Backwash 
Water 

Spent Media, Backwash 
Water 

Reject Water 

Other Considerations 

Possible pre & post pH 
adjustment. 
Pre-filtration required. 
Potentially hazardous brine 
waste. 

Nitrate peaking. 
Carbonate peaking affects pH. 

Possible pre & post pH 
adjustment. 

Pre-filtration may be 
required. 

Modified AA available. 

Media may be very 
expensive. 0 

Pre-filtration may be 
required. 

High water toss (15- 
75% of feed water) 

Centralized Cost 

Medium 

Medium 

Medium 

High 

POU Cost 

- 

Medium 

Medium 

Medium 


A Activated alumina is assumed to operate in a non-regenerated mode. 

B USEPA, 2002a. 

c IBS's track record in the US was not established enough to be considered as Best Available Technology (BAT) or Small System Compliance 
Technology (SSCT) at the time the rule was promulgated. 

D Affordable for systems with the given number of people served. 

E USEPA, 2000. 

F Pre-oxidation only required for As(HI). 

0 Some iron based sorbents may catalyze the As(III) to As(V) oxidation and therefore would not require a pre-oxidation step. 

H RO will remove As(IU), but its efficiency is not consistent and pre-oxidation will increase removal efficiency. 

1 AwwaRF, 2002. 

1 Kempie, 2002. 

K Wang, 2000. 

L AA can be used economically at higher pHs, but with a significant decrease in the capacity of the media. 

M Clifford, 2001. 

N Tumato, 2002. 

° With increased domestic use, IBS cost will significantly decrease. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


iv 


























Table ES-1. Arsenic Treatment Technologies Summary Comparison. 


(2 of 2) 



Precipitative Processes 

Factors 

Enhanced Lime 
Softening 

Enhanced 

(Conventional) 

Coagulation 

Filtration 

Coagulation- 

Assisted 

Micro- 

Filtration 

Coagulation- 
Assisted Direct 

Filtration 

Oxidation 

Filtration 


LS 

CF 

CMF 

CADF 

OxFilt 

USEPA BAT B 

Yes 

Yes 

No 

Yes 

Yes 

USEPA SSCT 8 

No 

No 

Yes 

Yes 

Yes 

System Size B D 

25-10,000 

25-10,000 

500-10,000 

500-10,000 

25-10,000 

SSCT for POU B 

No 

No 

No 

No 

No 

POU System Size BD 

- 

- 

- 

- 

- 

Removal Efficiency 

90% E 

95% (w/ FeClj) E 
< 90% (w/ Alum) E 

90% E 

90% E 

50-90% E 

Total Water Loss 

0% 

0% 

5% 

1-2% 

1-2% 

Pre-Oxidation Required F 

Yes 

Yes 

Yes 

Yes 

Yes 

Optimal Water 

Quality Conditions 

pH 10.5 - 11 1 
> 5 mgU Fe +JI 

pH 5.5 - 8.5 p 

pH 5.5 - 8.5 p 

pH 5.5 - 8.5 p 

pH 5.5 - 8.5 
>0.3 mg/L Fe 
FeAs Ratio > 20:1 

Operator Skill Required 

High 

High 

High 

High 

Medium 

Waste Generated 

Backwash Water, 
Sludge (high volume) 

Backwash Water, 
Sludge 

Backwash Water, 
Sludge 

Backwash Water, 
Sludge 

Backwash Water, 
Sludge 

Other Considerations 

Treated water requires pH 
adjustment. 

Possible pre & post 
pH adjustment. 

Possible pre & 
post pH 
adjustment. 

Possible pre & post 
pH adjustment. 

None. 

Centralized Cost 

Low Q 

Low Q 

High 

Medium 

Medium 

POU Cost 

N/A 

N/A 

N/A 

N/A 

N/A 


B USEPA, 2002a. 

D Affordable for systems with the given number of people served. 

E Depends on arsenic and iron concentrations. 

F Pre-oxidation only required for As(III). 

' AwwaRF, 2002. 
p Fields, et aL, 2002a. 

Q Costs for enhanced LS and enhanced CF are based on modification of an exisitng technology. Most small systems will not have this technology in 
place. 


Arsenic Treatment Technology’ Evaluation Handbook for Small Systems 


v 



























This page intentionally left blank. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


vi 



Contents 


EXECUTIVE SUMMARY./ 

CONTENTS.vii 

LIST OF FIGURES.a; 

LIST OF TABLES. xiii 

LIST OF ACRONYMS AND ABBREVIATIONS. xiv 

EQUATION NOMENCLATURE. jc vii 

1.0 BACKGROUND.1 

1.1 Purpose of this Handbook.1 

1.2 How to Use this Handbook.1 

1.3 Regulatory Direction.2 

1.3.1 The Arsenic Rule.2 

1.3.2 Health Effects.3 

1.3.3 Other Drinking Water Regulations.4 

1.3.4 Waste Disposal Regulations.5 

1.4 Arsenic Chemistry.8 

2.0 ARSENIC MITIGATION STRATEGIES.11 

2.1 Description of Arsenic Mitigation Strategies. 11 

2.1.1 Abandonment.12 

2.1.2 Seasonal Use.12 

2.1.3 Blending.13 

2.1.4 Treatment.15 

2.1.5 Sidestream Treatment.16 

2.2 Pre-Oxidation Processes.18 

2.2.1 Chlorine.19 

2.2.2 Permanganate.20 

2.2.3 Ozone.21 

2.2.4 Solid Phase Oxidants (Filox-R™).22 

2.3 Sorption Treatment Processes.23 

2.3.1 Ion Exchange.24 

2.3.2 Activated Alumina.26 

2.3.3 Iron Based Sorbents.29 

2.4 Membrane Treatment Processes.30 

2.5 Precipitation/Filtration Treatment Processes.32 

2.5.1 Enhanced Lime Softening.32 

2.5.2 Conventional Gravity Coagulation/Filtration.33 


Arsenic Treatment Technology Evaluation Handbook for Small Systems vii 







































2.5.3 Coagulation-Assisted Microfiltration 

2.5.5 Oxidation/Filtration. 

2.6 Point-of-Use Treatment. 


34 

35 
37 


3.0 ARSENIC TREATMENT SELECTION.39 

3.1 Selection Criteria.39 

3.1.1 Source Water Quality.39 

3.1.2 Process Evaluation Basis.41 

3.2 Process Selection Decision Trees.41 

4.0 PLANNING-LEVEL TREATMENT COSTS.55 

4.1 Pre-Oxidation System Costs Using Chlorine.57 

4.2 Ion Exchange System Costs.58 

4.3 Activated Alumina System Costs.63 

4.4 Iron Based Sorbent System Costs.68 

4.5 Greensand System Costs.68 

4.6 Coagulation Assisted Microfiltration System Costs.71 

4.7 Coagulation/Filtration System Enhancement Costs.74 

4.8 Lime Softening System Enhancement Costs.76 

4.9 Point-of-Use Reverse Osmosis System Costs.77 

4.10 Point-of-Use Activated Alumina System Costs.79 

4.11 Point-of-Use Iron Based Sorbent System Costs.80 

5.0 PRE-OXIDATION DESIGN CONSIDERATIONS.81 

5.1 Chlorine Pre-Oxidation Design Considerations.81 

5.1.1 Commercial Liquid Hypochlorite.82 

5.1.2 On-Site Hypochlorite Generation.84 

5.2 Permanganate Pre-Oxidation Design Considerations.86 

5.3 Ozone Pre-Oxidation Design Considerations.88 

5.4 Solid Phase Oxidant Pre-Oxidation Design Considerations.90 

5.5 Comparison of Pre-Oxidation Alternatives.93 

6.0 SORPTION PROCESS DESIGN CONSIDERATIONS.95 

6.1 Process Flow.95 

6.2 Column Rotation.96 

6.3 Sorption Theory.97 

6.3.1 Non-Regenerated Sorption Processes.98 

6.3.2 Ion Exchange Processes.98 

6.4 Process Design & Operational Parameters.100 

6.5 Column Design.101 

6.5.1 Column Diameter.102 

6.5.2 Column Height.103 

6.6 Media Replacement Frequency.104 

6.7 Regeneration of Ion Exchange Resin.105 

6.8 Waste Handling Systems.106 


Arsenic Treatment Technology Evaluation Handbook for Small Systems via 












































7.0 PRESSURIZED MEDIA FILTRATION PROCESS DESIGN CONSIDERATIONS ... 107 

7.1 Process Flow.107 

7.2 Process Design & Operational Parameters.109 

7.3 Filter Design.110 

7.3.1 Filter Diameter.113 

7.3.2 Media Weight. 113 

7.4 Waste Handling System Design. 114 

7.5 Coagulant Addition System Design. 115 

8.0 POINT-OF-USE TREATMENT.117 

8.1 Treatment Alternatives. 117 

8.1.1 Adsorption Point-of-Use Treatment. 117 

8.1.2 Reverse Osmosis Point-of-Use Treatment. 119 

8.2 Implementation Considerations.121 

8.2.1 Program Oversight.121 

8.2.2 Cost.122 

8.2.3 Compliance Monitoring.122 

8.2.4 Mechanical Warnings.122 

8.2.5 Operations and Maintenance.122 

8.2.6 Customer Education and Residential Access.123 

8.2.7 Residual Oxidant in Distribution System.123 

8.2.8 Waste Handling.123 

8.3 Device Certification.124 

9.0 REFERENCES.125 


Arsenic Treatment Technology’ Evaluation Handbook for Small Systems ix 

























List of Figures 


Figure 1-1. Optimal pH Ranges for Arsenic Treatment Technologies.4 

Figure 1-2. Flow Diagram for RO POU.8 

Figure 1-3. Dissociation of Arsenite [As(III)].9 

Figure 1-4. Dissociation of Arsenate [As(V)].9 

Figure 2-1. Example of Seasonal High Arsenic Source Use.13 

Figure 2-2. Blending.14 

Figure 2-3. Sidestream Treatment.16 

Figure 2-4. Treatment and Blending.16 

Figure 2-5. Sidestream Treatment and Blending.16 

Figure 2-6. Sidestream Treatment.17 

Figure 2-7. Sidestream Treatment for RO.17 

Figure 2-8. Ion Exchange Process Flow Diagram.24 

Figure 2-9. Effect of Sulfate on Ion Exchange Performance (Clifford, 1999). 25 

Figure 2-10. Activated Alumina Process Flow Diagram.27 

Figure 2-11. Effect of pH on Activated Alumina Performance.28 

Figure 2-12. RO Membrane Process Flow Diagram.30 

Figure 2-13. Two-Stage RO Treatment Process Schematic.31 

Figure 2-14. Generic Precipitation/Filtration Process Flow Diagram.32 

Figure 3-1. Decision Tree Overview.43 

Figure 3-2. Decision Tree 1 - Non-Treatment Alternatives.44 

Figure 3-3. Decision Tree 2 - Treatment Selection.45 

Figure 3-4. Decision Tree 2a - Enhanced Coagulation/Filtration.46 

Figure 3-5. Decision Tree 2b - Enhanced Lime Softening.47 

Figure 3-6. Decision Tree 2c - Iron/Manganese Filtration.48 

Figure 3-7. Decision Tree 3 - Selecting New Treatment.49 

Figure 3-8. Decision Tree 3a - Ion Exchange Processes.50 

Figure 3-9. Decision Tree 3b - Sorption Processes.51 

Figure 3-10. Decision Tree 3c - Filtration and Membrane Processes.52 

Figure 4-1. Chlorination Capital Costs.57 

Figure 4-2. Chlorination O&M Costs.58 

Figure 4-3. Ion Exchange (<20 mg/L S0 4 2 ') Capital Costs.59 

Figure 4-4. Ion Exchange (<20 mg/L S0 4 2 ) O&M Costs.59 

Figure 4-5. Ion Exchange (<20 mg/L S0 4 2 ) Waste Disposal Capital Costs.60 


X 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 





































Figure 4-6. Ion Exchange (<20 mg/L S0 4 2 ) Waste Disposal O&M Costs.60 

Figure 4-7. Ion Exchange (20-50 mg/L S0 4 2 ) Capital Costs.61 

Figure 4-8. Ion Exchange (20-50 mg/L S0 4 2 ') O&M Costs.61 

Figure 4-9. Ion Exchange (20-50 mg/L S0 4 2 ) Waste Disposal Capital Costs.62 

Figure 4-10. Ion Exchange (20-50 mg/L S0 4 2 ) Waste Disposal O&M Costs.62 

Figure 4-11. Activated Alumina (Natural pH) Capital Costs.63 

Figure 4-12. Activated Alumina (Natural pH of 7-8) O&M Costs.64 

Figure 4-13. Activated Alumina (Natural pH of 7-8) Waste Disposal O&M Costs.64 

Figure 4-14. Activated Alumina (Natural pH of 8-8.3) O&M Costs.65 

Figure 4-15. Activated Alumina (Natural pH of 8.0-8.3) Waste Disposal O&M Costs.65 

Figure 4-16. Activated Alumina (pH Adjusted to 6.0) Capital Costs.66 

Figure 4-17. Activated Alumina (pH adjusted to 6.0 - 23,100 BV) O&M Costs.66 

Figure 4-18. Activated Alumina (pH adjusted to 6.0 - 23,100 BV) Waste Disposal O&M 

Costs.67 

Figure 4-19. Activated Alumina (pH adjusted to 6.0 - 15,400 BV) O&M Costs.67 

Figure 4-20. Activated Alumina (pH adjusted to 6.0 - 15,400 BV) Waste Disposal O&M 

Costs.68 

Figure 4-21. Greensand Capital Costs.69 

Figure 4-22. Greensand O&M Costs.69 

Figure 4-23. Greensand Waste Disposal Capital Costs.70 

Figure 4-24. Greensand Waste Disposal O&M Costs.70 

Figure 4-25. Coagulation Assisted Microfiltration Capital Costs.71 

Figure 4-26. Coagulation Assisted Microfiltration O&M Costs.72 

Figure 4-27. Coagulation Assisted Microfiltration (w/ Mechanical Dewatering) Waste Disposal 

Capital Costs.72 

Figure 4-28. Coagulation Assisted Microfiltration (w/ Mechanical Dewatering) Waste Disposal 

O&M Costs.73 

Figure 4-29. Coagulation Assisted Microfiltration (w/ Non-Mechanical Dewatering) Waste 

Disposal Capital Costs.73 

Figure 4-30. Coagulation Assisted Microfiltration (w/ Non-Mechanical Dewatering) Waste 

Disposal O&M Costs.74 

Figure 4-31. Coagulation/Filtration System Enhancement Capital Costs.75 

Figure 4-32. Coagulation/Filtration System Enhancement O&M Costs.75 

Figure 4-33. Lime Softening Enhancement Capital Costs.76 

Figure 4-34. Lime Softening Enhancement O&M Costs.77 

Figure 4-35. POU Reverse Osmosis Capital Costs.78 


Arsenic Treatment Technology Evaluation Handbook for Small Systems xi 

































Figure 4-36. POU Reverse Osmosis O&M Costs.78 

Figure 4-37. POU Activated Alumina Capital Costs.79 

Figure 4-38. POU Activated Alumina O&M Costs.80 

Figure 5-1. Typical Liquid Hypochlorite Process Flow Diagram.83 

Figure 5-2. Liquid Hypochlorite System Schematic (USFilter, Wallace & Tieman).83 

Figure 5-3. Typical On-Site Hypochlorite Generation Process Flow Diagram.85 

Figure 5-4. On-Site Hypochlorite Generation System Schematic (USFilter, Wallace & 

Tieman).85 

Figure 5-5. On-Site Hypochlorite Generation System (Severn Trent Services).86 

Figure 5-6. Typical Permanganate Process Flow Diagram.87 

Figure 5-7. Permanganate Dry Feed System (Merrick Industries, Inc.).88 

Figure 5-8. Permanganate Dry Feed System (Acrison, Inc.).88 

Figure 5-9. Typical Ozonation Process Flow Diagram.89 

Figure 5-10. Ozone Generator and Contactor (ProMinent).90 

Figure 5-11. Typical Solid Phase Oxidant Arsenic Oxidation Process Flow Diagram.90 

Figure 5-12. Venturi Air Injector Assembly Schematic (Mazzei).91 

Figure 6-1. Sorption Treatment Process Flow Diagram w/o pH Adjustment and Regeneration. 95 
Figure 6-2. Sorption Treatment Process Flow Diagram w/ pH Adjustment and Regeneration. . 95 

Figure 6-3. Sorption Column Operation Modes.97 

Figure 6-4. Multi-Component Ion Exchange.98 

Figure 6-5. Activity of Nitrate and Nitrite During Ion Exchange.99 

Figure 6-6. Ion Exchange System (Tonka Equipment Company).102 

Figure 6-7. Process Flow Diagram for Example Problem.104 

Figure 7-1. Typical Media Filtration Process Flow Diagram.107 

Figure 7-2. Media Filtration Process Flow Modes.108 

Figure 7-3. Schematic of a Vertical Greensand Pressure Filter. 110 

Figure 7-4. Hub-Lateral Distribution System (Johnson Screens). 111 

Figure 7-5. Header-Lateral Distribution System (Johnson Screens). 111 

Figure 7-6. Multiple Media Filter Setup. 112 

Figure 7-7. Pressurized Media Filter (USFilter). 112 

Figure 7-8. Pre-Engineered Arsenic Filtration System (Kinetico). 113 

Figure 7-9. Ferric Chloride Addition Flow Diagram. 116 

Figure 8-1. Point-Of-Use Adsorption Setup (Kinetico). 118 

Figure 8-2. Metered Automatic Cartridge (Kinetico). 119 

Figure 8-3. Point-Of-Use Reverse Osmosis Setup (Kinetico).120 


Arsenic Treatment Technology Evaluation Handbook for Small Systems xii 



































List of Tables 


Table ES-1. Arsenic Treatment Technologies Summary Comparison. iv 

Table 1-1. Waste Disposal Options.6 

Table 2-1. Typical Treatment Efficiencies and Water Losses.16 

Table 2-2. Comparison of Oxidizing Agents.19 

Table 2-3. Water Quality Interferences with AA Adsorption.28 

Table 2-4. Examples of Iron Based Sorbents.29 

Table 3-1. Key Water Quality Parameters to be Monitored.40 

Table 3-2. Other Water Quality Parameters to be Monitored.41 

Table 3-3. Arsenic Treatment Technologies Summary Comparison.53 

Table 5-1. Typical Filox-R™ Design and Operating Parameters.92 

Table 5-2. Comparison of Pre-Oxidation Alternatives.93 

Table 6-1. Typical Sorption Treatment Design and Operating Parameters.101 

Table 7-1. Typical Greensand Column Design and Operating Parameters.109 


xiii 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


















List of Acronyms and Abbreviations 


AA 

Activated Alumina 

A1 

Aluminum 

ANSI 

American National Standards Institute 

As 

Arsenic 

As(III) 

Valence +3 Arsenic (found in Arsenite ion, AsO; 3 ) 

As(V) 

Valence +5 Arsenic (found in Arsenate ion, AsO; 3 ) 

AsO; 3 

Arsenite ion 

AsO; 3 

Arsenate ion 

ASTM 

American Society for Testing and Materials 

AWWA 

American Water Works Association 

AwwaRF 

American Water Works Association Research Foundation 

BAT 

Best Available Technology 

BV 

Bed Volume 

eft 

Cubic feet 

Ca +2 

Calcium 

CaCO, 

Calcium Carbonate 

CADF 

Coagulation-Assisted Direct Filtration 

CCI 

Construction Cost Index 

CF 

Enhanced (Conventional) Coagulation/Filtration 

ci- 

Chloride 

ci 2 

Chlorine 

CMF 

Coagulation-Assisted Microfiltration 

CO; 2 

Carbonate 

CT 

Disinfectant Concentration Times Contact Time 

CWA 

Clean Water Act of 1987 

DBP 

Disinfection By-Product 

DBPR 

Disinfectants/Disinfection By-Products Rule 

DO 

Dissolved Oxygen 

EBCT 

Empty Bed Contact Time 

ENR 

Engineering News Record 

F' 

Fluoride 

Fe, Fe +2 , Fe +3 

Iron 

FeCl 3 

Ferric Chloride 

Fe(OH) 3 

Ferric Hydroxide 

ft 

Feet 

FTW 

Filter-To-Waste 

g 

Gram 

gal 

Gallon 

GFH 

Granular Ferric Hydroxide 

gpd 

Gallons per Day 

gph 

Gallons per Hour 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


xiv 




gpm 

Gallons per Minute 

hr 

Hour 

H + 

Hydronium, Hydrogen ion 

H 2 AsO; 

Monovalent Arsenite Ion 

H,AsO " 

Monovalent Arsenate Ion 

H,0 

Water 

H,S 

Hydrogen Sulfide 

H“SO d 

Sulfuric Acid 

H^AsO, 

Arsenite Molecule 

H'AsO, 

Arsenate Molecule 

HAA5 

Haloacetic Acid 

HAsO; 2 

Divalent Arsenite Ion 

HAsO; 2 

Divalent Arsenate Ion 

HC1 

Hydrochloric Acid 

HOC1 

Hypochlorous Acid 

HS- 

Hydrogen Sulfide Ion 

IBS 

Iron Based Sorbents 

in. 

Inches 

IESWTR 

Interim Enhanced Surface Water Treatment Rule 

IX 

Ion Exchange 

kg 

kilogram 

kWh 

Kilowatt Hour 

L 

Liter 

LACSL 

Land Application Clean Sludge Limit 

lb(s) 

Pound(s) 

LCR 

Lead and Copper Rule 

LS 

Lime Softening 

LT IESWTR 

Long Term-1 Enhanced Surface Water Treatment Rule 

MCL 

Maximum Contaminant Level 

MF 

Micro-Filtration 

mg 

Milligram 

Mg 

Magnesium 

MGD 

Million Gallons per Day 

min. 

Minute 

mL 

Milliliter 

mm 

Millimeter 

Mn, Mn +2 

Manganese 

MnO, 

Manganese Dioxide 

MnO; 

Permanganate 

MSHA 

Mine Safety and Health Administration 

MTZ 

Mass Transfer Zone 

N 

Nitrogen 

NaCl 

Sodium Chloride 

NaOCl 

Sodium Hypochlorite 

NaOH 

Sodium Hydroxide 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


xv 



NIOSH 

National Institute for Occupational Safety and Health 

NIPDWRs 

National Interim Primary Drinking Water Regulations 

NO.- 

Nitrite 

NO; 

Nitrate 

NOM 

Natural Organic Matter 

NPDES 

National Pollutant Discharge Elimination System 

NPDWRs 

National Primary Drinking Water Regulations 

NTNC 

Non-Transient, Non-Community 

NTU 

Nephelometric Turbidity Units 

o 2 

Oxygen 

0 3 

Ozone 

O&M 

Operations and Maintenance 

oci- 

Hypochlorite 

OH 

Hydroxide 

PFLT 

Paint Filter Liquids Test 

pH 

Negative Log of Hydrogen Ion Concentration 

PO; 3 

Phosphate, Orthophosphate 

POE 

Point-of-Entry 

POTW 

Publicly Owned Treatment Works 

POU 

Point-of-Use 

psi 

Pounds per Square Inch 

RCRA 

Resource Conservation and Recovery Act 

RO 

Reverse Osmosis 

S° 

Sulfur, zero valence 

SBA 

Strong Base Anion exchange resin 

scf 

Standard Cubic Feet 

scfm 

Standard Cubic Feet per Minute 

SDWA 

Safe Drinking Water Act 

sft 

Square Feet 

Si(0H) 3 0 

Silicate Ion 

so 4 2 - 

Sulfate 

SSCT 

Small System Compliance Technologies 

SWTR 

Surface Water Treatment Rule 

TBLL 

Technically Based Local Limit 

TC 

Toxicity Characteristic 

TCLP 

Toxicity Characteristic Leaching Procedure 

TDS 

Total Dissolved Solids 

TTHM 

Total Trihalomethanes 

TOC 

Total Organic Carbon 

UFC 

Uniform Fire Code 

USEPA 

United States Environmental Protection Agency 

UV 

Ultra-Violet 

WET 

Waste Extraction Test 

wt% 

Weight Percent 

y 

Year 


Arsenic Treatment Technology’ Evaluation Handbook for Small Systems 


xvi 



Equation Nomenclature 






Symbol 

Definition 

Units 


BV 

e 

Number of Bed Volumes to Exhaustion 



^As,j 

Arsenic Concentration of Source j 

mg/L 


C As , B 

Arsenic Concentration of Blended Stream 

mg/L 


C C1 2 

Chlorine Concentration 

lbs Cl 2 /gal 


^FeClj 

Ferric Chloride Stock Solution Concentration 

wt% 


c. 

Concentration of Species i in the Feed Stream 

mg/L 


c k 

Arsenic Concentration Entering System During 
Quarter k 

mg/L 


c 

MCL 

Arsenic MCL 

mg/L 


c 

Mn0 4 

Permanganate Stock Solution Concentration 

mg/L 


c R , 

Concentration of Species i in the Retentate 

mg/L 


^RAA 

Running Annual Average Arsenic Concentration 

mg/L 


c 

TDS 

Concentration of Total Dissolved Solids 

g/L 


CCL t 

Current 

Construction Cost Index for the Current Year 

- 


CCI 

^^ A 1998 

Construction Cost Index for 1998 

- 


D 

Column Diameter 

ft 


Dq 2 

Ultimate Chlorine Demand 

mg/L as Cft 


^Mn0 4 

Ultimate Permanganate Demand 

mg/L as Mn 


D o, 

Ultimate Oxygen Demand 

mg/L 


Do, 

Ultimate Ozone Demand 

mg/L 


E 

Overall Rejection Rate 

% 


E s 

Individual Stage Contaminant Rejection Rate 

% 


EBCT 

Empty Bed Contact Time 

minutes 


F 

Freeboard Allowance 

% 


G bw 

Backwash Flux 

gpm/sft 


O r 

Regeneration Flux 

gpm/sft 


HLR 

Hydraulic Loading Rate 

gpm/sft 


H 

Column Height 

ft 


h 

J 

Height of Media Layer j 

ft 


i 

Annual Inflation Rate 

% 


ML. 

Bnne 

Brine Molarity 

mole/L 


M C1 2 

Chlorine Mass Flow 

lb/day of Cl 2 


Arsenic Treatment Technology > Evaluation Handbook for Small Systems 


xvii 








Symbol 

Definition 

Units 

Mq 3 

Ozone Mass Flow 

g/hr of 0 3 

n 

Number of Stages 

- 

n P 

Number of Parallel Treatment Trains 

- 

P 

1998 

Year 1998 Cost 

$ 

^Current 

Current Cost 

$ 

Q 

Design Flow Rate 

gpm 

Qj 

Flowrate of Source j 

gpm 

Qb 

Flowrate of Blended Stream 

gpm 

Qbw 

Backwash Flowrate 

gpm 

Qci 2 

Hypochlorite Metering Pump Rate 

gp h 

QFeClj 

Ferric Chloride Metering Pump Rate 

mL/min 

Q Mn0 4 

Permanganate Metering Pump Rate 

gph 

Q s 

Flowrate to be Split off and Treated 

gpm 

t 

Storage Time 

days 

^BW 

Backwash Duration 

minutes 

Vrw 

Filter-To-Waste Duration 

minutes 

*R 

Regeneration Duration 

minutes 

V 

Storage Volume 

gal 

V 

ww 

Volume of Wastewater 

gal 

w 

J 

Weight of Media j 

lbs 

^Current 

Current Year 

- 

z 

Depth of Media 

ft 

p 

Individual Stage Water Recovery Rate 

% 

^Cl 2 

Chlorine Dose 

mg/L as Cl 2 

^FeCl 3 

Ferric Chloride Dose 

mg/L 

^Mn0 4 

Permanganate Dose 

mg/L as Mn 

5 0 2 

Oxygen Dose 

mg/L 

^Oj 

Ozone Dose 

mg/L 

e 

Arsenic Rejection Rate 

% 

PFeCl 3 

Density of Ferric Chloride 

kg/L 

P, 

Bulk Density of Media j 

lbs/cft 

a 

Safety Margin 

% 

T 

Optimal Filter Run Time 

hr 

CO 

Treatment Water Loss 

% 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 





Section 1 
Background 


1.1 Purpose of this Handbook 


This Handbook is intended to serve as a resource for small municipal drinking water systems that 
may be affected by provisions of the Arsenic Rule. A “small” system is defined as a system serving 
10,000 or fewer people. Average water demand for these size systems is normally less than 1.4 
million gallons per day (MGD). Please note that the USEPA statutes and regulations described in 
this document contain legally binding requirements. The recommendations provided in this hand¬ 
book do not substitute for those statutes or regulations, nor is this document a regulation itself. The 
approaches described in this handbook are strictly voluntary and do not impose legally-binding 
requirements on USEPA, states, local or tribal governments, or members of the public, and may not 
apply to a particular situation based upon the circumstances. Although the USEPA strongly recom¬ 
mends the approach outlined in this document, state and local decision makers are free to adopt 
approaches that differ from this handbook or to evaluate and choose technologies that are not dis¬ 
cussed here. Interested parties are free to raise questions and objections about the appropriateness 
of the application of this handbook. Any USEPA decisions regarding a particular system will be 
made based on the applicable statutes and regulations. The USEPA may review and update this 
handbook as necessary and appropriate. 

1.2 How to Use this Handbook 

This Handbook includes general arsenic treatment information, cost evaluation tools, and design 
considerations for specific treatment technologies. The Handbook is organized to enable the utility 
to make educated decisions about the most appropriate treatment approach(es) to address arsenic 
concerns prior to getting involved in detailed design considerations. The utility should read Sec¬ 
tions 1 through 3 in sequence, then use the treatment selection guidance provided in Section 3 to 
determine the most appropriate cost and design considerations sections (Sections 4 through 8). 

Section 1 provides background information on the Arsenic Rule, waste disposal regulation, and 
arsenic chemistry that is useful in understanding the remainder of the Handbook. 

Section 2 provides descriptions and background information for established arsenic mitigation strat¬ 
egies, with emphasis on those that are most technically and financially suitable for small systems. 
The utility should use this section to gather background information on the various arsenic mitiga¬ 
tion strategies and determine the flowrate to be treated if treatment is selected as the mitigation 
strategy. 

Section 3 describes the considerations required to make an informed treatment method selection. 
Decision trees are provided to guide the utility to the most applicable mitigation or treatment strat- 


Arsenic Treatment Technology- Evaluation Handbook for Small Systems 


1 





egy. The selected process is the one that has the highest chance of achieving the most cost effective 
solution for the particular water source, given the parameters used in the decision making process. 

Section 4 enables the utility to quickly estimate the planning-level costs for the selected treatment 
process. This section is intended for those utilities that have identified the need to install new 
arsenic treatment. Based on the cost estimate, the utility can then decide if the selected treatment 
process is economically feasible. If it is not, the utility can repeat the decision trees and apply 
different preferences. It is important to recognize that the cost curves provided are for planning- 
level considerations only and should not be used as the primary decision-making tools. 

Section 5 presents pre-oxidation alternatives and design calculations. This section is relevant to 
those utilities that have selected a treatment alternative and do not currently employ oxidation at the 
source(s) with arsenic concerns. 

Sections 6-8 are intended for those utilities that have identified the need to install new arsenic 
treatment technologies. These sections provide design information on each of the primary arsenic 
treatment technologies. 

After the selected mitigation strategy has been reviewed, the utility should evaluate the cost and 
constraints of the mitigation strategy. For strategies that involve modification of an existing pro¬ 
cess, a test should be run. For strategies that involve a new process, a pilot plant test should be run. 
After the tests have been performed and the results analyzed, the utility should re-evaluate whether 
the strategy will reduce the arsenic concentration below the Maximum Contaminant Level (MCL). 

1.3 Regulatory Direction 

1.3.1 The Arsenic Rule 

The former arsenic MCL was 0.05 mg/L, as established under the 1975 National Interim 
Primary Drinking Water Regulations (NIPDWRs). As part of the 1996 Safe Drinking Wa¬ 
ter Act (SDWA) Amendments, the United States Environmental Protection Agency (USEPA) 
was directed to conduct health effects and cost/benefit research to finalize a new arsenic 
standard. 

In June 2000, the USEPA proposed a revised arsenic MCL of 0.005 mg/L, and requested 
public comment on alternative MCLs of 0.003, 0.010, and 0.020 mg/L. The USEPA pub¬ 
lished a final rule in the Federal Register in January 2001 (USEPA, 2001). This rule estab¬ 
lished a revised arsenic MCL of 0.010 mg/L, and identified the following as Best Available 
Technologies (BATs) for achieving compliance with this regulatory level: 

• Ion Exchange (IX) 

• Activated Alumina (AA) 

• Oxidation/Filtration 

• Reverse Osmosis (RO) 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


2 



• Electrodialysis Reversal 

• Enhanced Coagulation/Filtration 

• Enhanced Lime Softening 

The following are listed in the final rule and the Implementation Guidance for the Arsenic 
Rule (USEPA, 2002a) as Small System Compliance Technologies (SSCT). 

• IX 

• AA, centralized and point-of-use (POU) 

• RO, centralized and POU 

• Electrodialysis Reversal 

• Oxidation/Filtration 

• Coagulation/Filtration, Enhanced Coagulation/Filtration, and Coagulation-Assisted 
Microfiltration (CMF) 

• Lime Softening (LS) and Enhanced Lime Softening 

This regulation applies to all community water systems and non-transient, non-community 
(NTNC) water systems, regardless of size. Please note that systems are not required to use 
these technologies. 

Compliance with the Arsenic Rule will be required by January 2006. The running annual 
average arsenic level must be at or below 0.010 mg/L at each entry point to the distribution 
system. However, POU treatment can be instituted instead of centralized treatment. Ana¬ 
lytical results for arsenic are rounded to the nearest 0.001 mg/L for reporting and compli¬ 
ance determination. 

1.3.2 Health Effects 

Motivation to reduce the arsenic MCL is driven by the findings of health effects research. 
Over the past several years, numerous toxicological and epidemiological studies have been 
conducted to ascertain health risks associated with low-level exposure to As(V) ingestion. 

Ingestion of inorganic arsenic can result in both cancer and non-cancer health effects (NRC, 
1999). Arsenic interferes with a number of essential physiological activities, including the 
actions of enzymes, essential cations, and transcriptional events in cells (NRC, 1999). The 
USEPA has classified arsenic as a Class A human carcinogen. Chronic exposure to low 
arsenic levels (less than 0.05 mg/L) has been linked to health complications, including 
cancer of the skin, kidney, lung, and bladder, as well as other diseases of the skin, neurologi¬ 
cal, and cardiovascular system (USEPA, 2000). 

The primary mode of exposure is ingestion of water containing arsenic. Dermal absorption 
of arsenic is minimal; therefore, hand washing and bathing do not pose a known risk to 
human health. 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


3 




1.3.3 Other Drinking Water Regulations 

In an attempt to comply with one drinking water regulation, it is possible to compromise 
treatment performance or compliance with other drinking water regulations. Therefore, in 
an effort to conform with the Arsenic Rule, community water systems should be cognizant 
of potential system-wide, regulatory, and operational impacts. In particular, compliance 
with the following regulations should be considered. 

• Lead and Copper Rule (LCR) 

• Surface Water Rules (SWTR, IESWTR, LT1ESWTR) 

• Disinfectants/Disinfection By-Products Rule (DBPR) 

Many of the arsenic treatment technologies require pH adjustment for optimization of 
performance. Figure 11 provides a summary of the optimal pH ranges for several arsenic 
treatment technologies. Sorption and coagulation processes are particularly sensitive to 
pH, and function most effectively at the lower end of the natural pH range. However, use of 
AA at a natural pH may be a cost effective option for many small water systems. 


Enhanced Lime Softening 

j Reverse Osmosis 

__________ Anion Exchange 

__ Iron Based Sorbents 

_ Oxidation Filtration 

______ Conventional Activated Alumina 

_ Enhanced Iron Coagulation 

bM Enhanced Aluminum Coagulation 

l_I_I_I_l_I_l 

5 6 7 8 9 10 11 

pH 


Figure 1-1. Optimal pH Ranges for Arsenic Treatment Technologies. 

In addition to affecting arsenic treatability, pH also can have a significant effect on disinfec¬ 
tion, coagulation, and chemical solubility/precipitation within the distribution system and 
in plumbing systems (LCR). 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


4 





























Lead and Copper Rule 

Lead and copper in tap water is primarily due to corrosion of plumbing system components 
within buildings, including copper pipes, lead-based solder used to join segments of copper 
pipe, and faucets made from brass. Alkalinity and pH play a critical role in providing 
passivation protection from corrosion. In general, the optimum pH range for minimizing 
corrosion of lead and copper is 7.59.0. Therefore, post-treatment pH adjustment is recom¬ 
mended for many of the treatment techniques provided in Figure 11. 

Surface Water Rules (SWTR, IESTWR, LT1ESWTR) 

Disinfection efficacy is also related to pH if chlorine is used. When pre-chlorinating, the 
biocidal potential of chlorine is enhanced as the pH is reduced. Therefore, utilities that are 
currently required to meet a CT (disinfectant concentration times contact time) standard 
should receive disinfection benefit from pH reduction at the head of the treatment process. 
Post-treatment pH adjustment for corrosion control should be conducted after CT require¬ 
ments are met. 

Coagulation and flocculation processes are also related to pH. The formation of floe is 
improved as the pH is reduced, and optimized within the range of 5-8. However, iron and 
aluminum-based coagulants also consume alkalinity, thereby decreasing the buffering ca¬ 
pacity of the water. 

Disinfectants/Disinfection By-Products Rule (DBPR) 

Chlorine reacts with natural organic matter (NOM) to form halogenated disinfection by¬ 
products, such as total trihalomethanes (TTHM) and haloacetic acids (HAA5). Therefore, 
incorporating pre-chlorination to convert As(III) to As(V) could increase the occurrence of 
these regulated chemicals. However, as most arsenic in surface water is already oxidized to 
As(V), chlorination may not be necessary in surface water, where disinfection byproducts 
are of the most concern. The Stage 1 DBPR 1 establishes running annual average MCLs of 
0.080 mg/L and 0.060 mg/L for TTHM and HAA5, respectively. 

The Stage 2 DBPR, scheduled for proposal in early 2003, augments the Stage 1 DBPR to 
reduce health risks from DBP exposure. 

1.3.4 Waste Disposal Regulations 

Waste disposal is an important consideration in the treatment selection process. Arsenic 
removal technologies produce several different types of waste, including sludges, brine 
streams, backwash slurries, and spent media. These wastes have the potential for being 
classified as hazardous and can pose disposal problems. Table 1-1 provides a summary of 
the available waste disposal options and associated criteria. These are further discussed in 
the following paragraphs. In addition, specific waste disposal considerations for each tech¬ 
nology are discussed in Section 2. 

1 The Stage 1 DBPR became effective for surface water systems and groundwater systems under the direct 
influence of surface water serving at least 10,000 people in January 2002. The rule will take effect for all 
groundwater systems, and surface water systems and groundwater systems under the direct influence of surface 
water systems serving less than 10,000 people in January 2004. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


5 




Table 1-1. Waste Disposal Options. 

Waste Type 

Disposal Method (Criteria) 


• Direct Discharge to Surface Water (CWA, NPDES) 

• Indirect Discharge to POTW (TBLLs) 

• On-Site Sewerage (POU systems) 

Liquid 

• Infiltration to Ground Water 

• Evaporation Ponds 

• Recycle/Reuse 

• Ocean Discharge 


• Land Application 

Solid (sludge, media) 

• Municipal Solid Waste Landfill (PFLT, TCLP, WET in California) 

• Hazardous Waste Landfill (PFLT) 


Liquid waste streams must have lower concentrations than the Toxicity Characteristic (TC) 
in order for the waste to be classified as non-hazardous. The arsenic TC is 5.0 mg/L. Those 
liquid waste streams that contain more than 5.0 mg/L of arsenic would therefore be classi¬ 
fied as a hazardous waste. Many of the arsenic removal technologies also remove other 
constituents (e.g., chromium). The waste stream must be analyzed for these other sub¬ 
stances that may be in concentrations above their respective TCs. Because of Resource 
Conservation and Recovery Act (RCRA) requirements and cost implications, on-site treat¬ 
ment or off-site disposal of hazardous waste is likely to be infeasible for small water sys¬ 
tems. Indirect discharge may be an option since wastes that pass through a sewer system to 
a Publicly Owned Treatment Works (POTW) are exempt from RCRA regulation once the 
waste mixes with wastewater from the sewer. Utilities considering indirect discharge should 
work with the POTW to determine if the arsenic waste levels would be acceptable to a 
revised Technically Based Local Limit (TBLL). (The TBLL would be revised because the 
arsenic treatment will change the arsenic background at the POTW). 

Solids waste streams are subject to the Toxicity Characteristic Leaching Procedure (TCLP). 
This test is used to simulate the potential for leaching in a landfill setting. The TCLP 
leachate must be lower than any of the TC values in order for the waste to be classified as 
non-hazardous. 

There are five realistic methods for the disposal of arsenic waste streams. 

Landfill Disposal 

Historically, municipal solid waste landfills have been commonly used for the disposal of 
non-hazardous solid wastes emanating from treatment processes. However, the hazard po¬ 
tential of arsenic may limit the feasibility of this alternative. 

Dewatered sludge and spent media can be disposed in a municipal solid waste landfill if the 
waste passes both the Paint Filter Liquids Test (PFLT) and the TCLP. The PFLT is used to 
verify there is no free liquid residual associated with the waste. However, if the TCLP 
extract contains arsenic or any other contaminant (e.g., chromium) above the TC, the waste 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


6 









residuals must be disposed in a designated and licensed hazardous waste landfill. These 
landfills are strictly regulated under RCRA and have extensive monitoring and operational 
guidelines. As such, the costs of disposal are relatively high. As with municipal solid waste 
landfill disposal, waste sludges must not contain free liquid residuals. 

A critical element of hazardous waste disposal is the cradle-to-grave concept. The party 
responsible for generating the hazardous waste retains liability and responsibility for the 
fate and transport of the waste. 

Direct Discharge to Surface Waters 

Direct discharge refers to the disposal of liquid waste streams to nearby surface waters, 
which act to dilute and disperse the waste by-products. The primary advantage of direct 
discharge is reduced capital and operations and maintenance (O&M) costs due to the elimi¬ 
nation of residuals treatment. The feasibility of this disposal method is subject to provi¬ 
sions of the National Pollution Discharge Elimination System (NPDES) and state anti-deg¬ 
radation regulation. The allowable discharge is a function of the ability of the receiving 
water to assimilate the arsenic without exceeding water quality criteria established under 
the Clean Water Act (CWA) or state regulation. Different water quality criteria exist de¬ 
pending on the classification of the receiving water. For specific NPDES conditions and 
limits, the appropriate NPDES permitting agency should be contacted, because the condi¬ 
tions and limits can vary according to the receiving stream’s particular characteristics. 

Indirect Discharge 

The discharge of liquid waste streams to a POTW is a potential disposal alternative. In this 
case, the waste stream will be subject to TBLLs established regionally by sewer authorities 
as part of the POTW’s Industrial Pretreatment Program. TBLLs are established in order to 
protect POTW operation, assure compliance with NPDES permits, and prevent an unac¬ 
ceptable level of accumulation of contaminants in the process sludge and biosolids. The 
arsenic limit is usually on the order of 0.05 to 0.1 mg/L. The TBLLs are computed for each 
POTW to take into account the background levels of contaminants in the municipal waste- 
water. The background level will change because of the drinking water treatment process, 
which may lead to revised TBLLs. The revised TBLL would be used to determine if the 
liquid waste stream could be discharged to the POTW. 

Land Application 

Land application of concentrated sludge may be allowed under certain conditions depend¬ 
ing on the state law and regulations. Some states do not allow land application of solid 
residuals. Sewage sludge (also called “biosolids”) containing <41 mg As/kg biosolids can 
be land-applied with no restrictions. Biosolids with arsenic concentrations between 41 and 
75 mg/kg can be land-applied, but must track arsenic accumulation. The lifetime arsenic 
accumulation limit is 41 kg As per hectare of land. Federal part 503 land application limits 
are only applicable in states that have adopted these limits for water plant residuals or in 
cases where these residuals are mixed with sewage sludge. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


7 



On-Site Sewerage 

Liquid waste streams from RO POU devices should be suitable for disposal in an on-site 
sewerage or septic system. Figure 1-2 illustrates a typical flow diagram for RO POU water 
treatment and on-site waste disposal. 


Non-Consumptive 

Water 


From Water 
Supply 



Figure 1-2. Flow Diagram for RO POU. 


Arsenic is concentrated in the RO retentate during normal process operation. However, 
eventually this retentate is combined with other domestic wastewater in the septic tank. 
Because the amount of water consumed is small relative to the total flow entering the dwell¬ 
ing, the concentration of arsenic in the blended wastewater is nearly identical to that in the 
influent stream. 

1.4 Arsenic Chemistry 


Arsenic is introduced into the aquatic environment from both natural and manmade sources. Typi¬ 
cally, however, arsenic occurrence in water is caused by the weathering and dissolution of arsenic¬ 
bearing rocks, minerals, and ores. Although arsenic exists in both organic and inorganic forms, the 
inorganic forms are more prevalent in water and are considered more toxic. Therefore, the focus of 
this Handbook is on inorganic arsenic. 

Total inorganic arsenic is the sum of particulate and soluble arsenic. A 0.45-micron filter can 
generally remove particulate arsenic. 

Soluble, inorganic arsenic exists in either one of two valence states depending on local oxidation- 
reduction conditions. Typically groundwater has anoxic conditions and arsenic is found in its ars- 
enite or reduced trivalent form [As(III)]. Surface water generally has aerobic conditions and ar¬ 
senic is found in its arsenate or oxidized pentavalent form [As(V)]. 

Both arsenite and arsenate exist in four different species. The speciation of these molecules changes 
by dissociation and is pH dependent. The kinetics of dissociation for each are nearly instantaneous. 
The pH dependencies of arsenite and arsenate are depicted in Figure 1-3 and Figure 1-4, respec- 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


8 













tively. The species shown in bold are those that are most likely to be removed by the techniques 
discussed in this handbook. 



0 2 4 6 8 10 12 14 

pH 

Figure 1-3. Dissociation of Arsenite [As(III)]. 



Figure 1-4. Dissociation of Arsenate [As(V)]. 

Chemical speciation is a critical element of arsenic treatability. Negative surface charges facilitate 
removal by adsorption, anion exchange, and co-precipitative processes. Since the net charge of 
arsenite [As(III)] is neutral at natural pH levels (6-9), this form is not easily removed. However, the 
net molecular charge of arsenate [As(V)] is negative (-1 or -2) at natural pH levels, enabling it to be 
removed with greater efficiency. Conversion to As(V) is a critical element of most arsenic treat¬ 
ment processes. This conversion can be accomplished by adding an oxidizing agent such as chlo¬ 
rine or permanganate. Selection of the most appropriate oxidation technology should be based on 
several considerations, including cost, integration with existing treatment, disinfection require¬ 
ments, and secondary effects. This is discussed further in Section 2.2. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


9 



































This page intentionally left blank. 


Arsenic Treatment Technology' Evaluation Handbook for Small Systems 


10 



Section 2 

Arsenic Mitigation Strategies 

2.1 Description of Arsenic Mitigation Strategies 

Problematic arsenic levels in drinking water can be mitigated in several different ways. This Hand¬ 
book will address the following mitigation strategies: 

• Abandonment - The total abandonment of the problematic source(s) and subsequent switch to 
other source(s) within the system or purchase from a neighboring system. 

• Seasonal Use - Switching the problematic source(s) from full-time used to seasonal or peaking 
use only with subsequent blending with other full-time source(s). 

• Blending - The combination of multiple water sources to produce a stream with an arsenic 
concentration below the MCL. 

• Sidestream Treatment - The treatment of a portion of the high arsenic water stream and subse¬ 
quent blending back with the untreated portion of the stream to produce water that meets the 
MCL. 

• Treatment - The processing of all or part of a water stream to reduce the arsenic concentration 
to below the MCL. 

O Wellhead Treatment - Treatment is located at the wellhead location before the water is 
mixed with water from other sources. 

O Centralized Treatment - Water from several sources is piped to a centralized location for 
treatment before the water enters the distribution system. 

O POU Treatment - Treatment devices are located at the Point-Of-Use within the building or 
home and treat only the water intended for direct consumption, typically at a single tap. 

There are three primary categories of available treatment processes. 

• Sorption Treatment Processes 
O IX 2 

O AA 2 ’ 3 

O Iron Based Sorbents (IBS) 4 

• Membrane Treatment Processes 
O RO 2 ’ 3 

O Precipitation/Filtration Processes 

2 Technologies that have been designated as small system compliance technologies (SSCT) for centralized or 
wellhead treatment. 

3 Technologies that have been designated as SSCT for POU treatment. 

4 Due to limited performance research at the time the rule was promulgated, IBS was not designated as a BAT or a 
SSCT by the USEPA. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


11 





O Enhanced Conventional Gravity Coagulation/Filtration 2 above 
O CMF 2 above 

O Coagulation-Assisted Direct Filtration (CADF) 2 above 
O Oxidation/Filtration 2 above 
Q Enhanced Lime Softening 2 above 

The selection of the most appropriate mitigation strategy should be based on feasibility issues, 
system constraints, and costs. 

2.1.1 Abandonment 

Perhaps the simplest approach for remedying a high arsenic source is abandonment of the 
high arsenic water source and procurement of a new source that meets the arsenic MCL. 
This option is most realistic for utilities with multiple water sources where at least one 
source can be relied upon for producing water with arsenic below the MCL. There may, 
however, be other constraints to switching primary sources, such as inadequate treatment 
capacity or water rights. Many small systems do not have the flexibility to switch to a 
source with a lower arsenic concentration. In this particular case, the utility has two op¬ 
tions: (1) locate or install a new source, or (2) purchase water from a nearby system if an 
interconnection exists. New source installations may or may not be more costly than treat¬ 
ment. It should also be noted that drilling a new source may not be the best option if the 
aquifer has consistently high levels of arsenic. The utility should check with other systems 
in the area before drilling. 

2.1.2 Seasonal Use 

Another option is to switch a high arsenic water source from full-time production to sea¬ 
sonal or peaking use only. When used, it would be blended with low arsenic water sources 
before entry to the distribution system. This is allowed at the federal level, as long as the 
running annual average at the entry point to the distribution system does not exceed the 
MCL. Individual state requirements may preclude this option. 

The running annual average can be calculated by adding the four most recent quarterly 
arsenic concentrations together and dividing by 4 as seen in the following equation. 


C 


RAA ~ 


Cj + C2 + C3 + C4 
4 


Eqn. 2-1 


Where: 

C RA4 = Running Annual Average Arsenic Concentration Entering System, 
Cj = Arsenic Concentration Entering System During the Quarter 1, 

C, = Arsenic Concentration Entering System During the Quarter 2, 

C 3 = Arsenic Concentration Entering System During the Quarter 3, and 

C 4 = Arsenic Concentration Entering System During the Quarter 4. 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


12 




An example of this is shown in Figure 2-1. Well 1 is the only source for the first and second 
quarters of year and has an arsenic concentration of 0.003 mg/L. Well 2 is used in conjunc¬ 
tion with Well 1 for the third and fourth quarters of the year and the combined output from 
Wells 1 and 2 has an arsenic concentration of 0.014 mg/L. The running annual average is 
calculated below as 0.009 mg/L and complies with the federal Arsenic Rule. 


0.003 + 0.003 + 0.014 + 0.014 


RAA 


= 0.0085 mg/L 


0.009 mg/L 


Quarter 1 Quarter 2 Quarter 3 Quarter 4 


Well 1 




Flow To 
Distribution 
System 


(wan) 

n 

Flow To 
Distribution 
System 


(WenT) 

hr 

Flow To 
Distribution 
System 



▼ 

Flow To 
Distribution 
System 


Figure 2-1. Example of Seasonal High Arsenic Source Use. 

2.1.3 Blending 

The revised arsenic MCL must be met at all entry points to the distribution system. There¬ 
fore, blending is a viable mitigation strategy for conservative inorganic substances and should 
be considered by systems that utilize multiple sources. Blending involves mixing waters 
from two or more different sources prior to entering the distribution system. The purpose of 
blending is to eliminate the need for treatment. 

Stand-alone blending shown in Figure 2-2 is only a consideration when a water system has 
multiple sources, one (or more) with arsenic levels above the MCL, and one (or more) with 
arsenic levels below the MCL. Also, the wells with low arsenic levels must be reliable on 
a continuous basis. 

Each stream in the blending process should have a flow measurement to insure that the 
streams are blended in a ratio that produces an arsenic concentration that meets the MCL 
requirement. Flow measurement is shown in the following figure and an “F” inscribed in a 
circle. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


13 













Figure 2-2. Blending. 


The concentration of the blended stream (C AsB ) can be calculated using the following 
formula. 


^ Ql C As,l +Q 2 C As,2 

Ac R 

Q1+Q2 

Where: 

C As = Arsenic Concentration of Blended Stream (mg/L), 
C As = Arsenic Concentration of Well 1 (mg/L), 

C. _ = Arsenic Concentration of Well 2 (mg/L), 

Q = Flowrate of Well 1 (gpm), and 

Q, = Flowrate of Well 2 (gpm). 


Eqn. 2-2 


For example, suppose that water from Wells 1 and 2 in Figure 2-2 contain arsenic concen¬ 
trations of 0.015 mg/L and 0.006 mg/L, respectively, with flowrates of 700 gpm and 2,450 
gpm, respectively. The blended stream’s arsenic concentration will then be 0.008 mg/L, 
which meets the MCL, and is calculated as follows: 


L as,b 


700 gpm 0.015 mg / L + 2,450 gpm • 0.006 mg / L 
700 gpm + 2,450 gpm 


= 0.008 mg/L 


The following equation can be used to determine the required flowrate from the low arsenic 
source (Q2) that, when blended with flow from the high arsenic source (Ql), will produce 
water with an arsenic concentration a safe margin below the MCL. 


Where: 


Q. 

Q 2 

c. 


S 


Q2 -Qi ■ 


[l-q] C MCL -C As j 
C As,2 - &-°] C M €L 


A 

) 


= Flowrate of Well 1 (gpm) {high arsenic source}, 

= Flowrate of Well 2 (gpm) {low arsenic source}, 

= Arsenic Concentration of Well 1 (mg/L) {high arsenic source}, 
= Arsenic Concentration of Well 2 (mg/L) {low arsenic source}, 
= Arsenic MCL (mg/L), and 
= Safety Margin (% expressed as a decimal). 


Eqn. 2-3 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


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For example, suppose that water from Wells 1 and 2 in Figure 2-2 contain arsenic concen¬ 
trations of 0.015 mg/L and 0.006 mg/L, respectively. Assuming that the utility wants to 
provide a 20% safety margin (i.e., produce water with 0.008 mg/L of arsenic) and the maxi¬ 
mum flowrate from Well 1 is 700 gpm, the minimum required flowrate from Well 2 is 2,450 
gpm and is calculated as follows: 


Q 2 = 700 gpm- 


' [l - 0.2]- 0.010 mg/L - 0.015 mg/L > 
0.006 mg/L - [l - 0.2]- 0.010 mg/L 


= 2,450 gpm 


2.1.4 Treatment 

If a treatment method is used to mitigate the arsenic problem from multiple sources, the 
utility will need to decide between wellhead treatment and centralized treatment. Wellhead 
treatment treats the water from each well at or near the wellhead. For systems with multiple 
wells, this could result in multiple treatment facilities. If possible, piping high arsenic water 
from multiple sources to a single, centralized treatment facility may be more economical. 
Some factors to take into account would be: 

• the proximity of wells to be treated to each other, 

• feasibility of piping the sources to a central location, 

• availability of land and power at the treatment site(s), and 

• labor requirements for multiple sites rather than a single site. 

Some treatment processes (e.g., RO) may have significant water losses associated with 
them. Water loss is incoming water that does not exit the system as treated water. Water 
losses frequently occur as a stream used to dispose of waste. Typical treatment efficiencies 
and water losses for processes operated under normal conditions are provided in Table 2-1. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


15 







Table 2-1. Typical Treatment Efficiencies and Water Losses. 

Treatment 

As(V) Removal Efficiency 

Water Loss 

Sorption Processes 



Ion Exchange 

95% 1 

1-2% 

Activated Alumina (Throw-Away Media) 

95% 1 

1-2% 

Iron Based Sorbents 

Up to 98% 1 

1-2% 

Iron and Manganese Removal Processes 



Oxidation/Filtration (Greensand) 

50-90% 2 

<2% 


Membrane Processes 

Reverse Osmosis >95% 1 15-50% 1 


Precipitative Processes 


Coagulation Assisted Micro filtration 

Enhanced Coagulation/Filtration 

90% 1 

5% 

With Alum 

<90% 1 

1-2% 

With Ferric Chloride 

95% 1 


Enhanced Lime Softening 

90% ] 

1-2% 

1 USEPA, 2000. 


2 Depends on arsenic and iron concentrations 


2.1.5 Sidestream Treatment 

The treatment and blending strategies can be combined in a variety of ways as illustrated in 
Figure 2-3 through Figure 2-5. 



i 


Total Flow 

To Distribution System 


Well 1 


Treatment 


© 


~(5 


Blending 


V 

Total Flow 

To Distribution System 


Well 1 


CD 




Treatment 

(b 


Blending 


I 


Total Flow 

To Distribution System 


Figure 2-3. Sidestream 
Treatment. 


Figure 2-4. Treatment and 
Blending. 


Figure 2-5. Sidestream 
Treatment and Blending. 


Sidestream treatment, Figure 2-3, involves splitting the source flow, treating one stream, 
and then blending it with the untreated stream prior to distribution. Sidestream treatment is 
feasible when a water source exceeds the revised MCL by a relatively small margin. This 
approach is viable because most arsenic treatment processes (operated under optimal con¬ 
ditions) can achieve at least 80% arsenic removal and, in many cases, this high level of 


Arsenic Treatment Technology’ Evaluation Handbook for Small Systems 


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performance is not needed to meet the MCL. Any utility considering treatment should 
consider sidestream treatment as a method to reduce the overall level and cost of the treat¬ 
ment required. 

In the simple case of sidestream treatment from a single source, as in Figure 2-6, the flowrate 
of the split stream requiring treatment can be calculated using Equation 2-4. If the treat¬ 
ment process is RO, as in Figure 2-7, the flowrate of the split stream requiring treatment can 
be calculated using Equation 2-5. RO requires a more complex equation because RO has a 
continuous stream of water lost during operation and this water is not available for blend¬ 
ing. In all the other treatments, when the water loss occurs (e.g., the backwash of a column 
or filter) no treated water is available for blending so no blending occurs. (Under these 
circumstances, the untreated water flow to the distribution is also halted.) For all the treat¬ 
ment methods, the resulting blended treated flowrate can be calculated using Equation 2-6. 


^ ^ { c i -(l-o)-C MCL 

VS -VI -“— — 


Eqn. 2-4 



Eqn. 2-5 


Qb - Qi -®Qs 


Eqn. 2-6 


The variable for the equations are: 

Q s = Flowrate to Split Off for Treatment (gpm), 

Q b = Flowrate of the Final Blended Stream (gpm), 

Q t = Source 1 Flowrate (gpm), 

C, = Arsenic Concentration of the Source (mg/L), 

C mcl = Arsenic MCL (mg/L), 

a = Safety Margin (% expressed as a decimal), 

co = Treatment Water Loss (% expressed as a decimal), and 

8 = Arsenic Rejection Rate (% expressed as a decimal). 


Source 

Water 


Source 

Water 




Treatment i r 
By-Pass 



Treatment i ' 
By-Pass 



Treatment 
Water Loss 


^ Qb’ ^mcl 

Blended 
Treated Water 


^ Qb’ Cmcl 

Blended 
Treated Water 


Figure 2-6. Sidestream Treatment. Figure 2-7. Sidestream Treatment for RO. 


Arsenic Treatment Technology’ Evaluation Handbook for Small Systems 


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For example, suppose a water utility operates a single well at a maximum flowrate (Q,) of 
500 gpm. The well water contains (C,) 0.012 mg/L of arsenic. Further, assume that utility 
wants to provide a 20% safety margin (a) on the arsenic MCL (C MCL ) of 0.010 mg/L (i.e., 
produce water with 0.008 mg/L of arsenic). The utility has selected a RO process that has 
demonstrated an arsenic removal efficiency (£) of 95% at a water loss (co) of 40%. Using 
Equation 2-5, 237 gpm of the well’s flow (or approximately 47%) should be split and sent 
to the RO treatment unit. The final (blended) flowrate is 405 gpm, as determined using 
Equation 26. 


Qs = ( 500 gP m )- 


r _ 0.012 mg/L -[l- 0.2]-0.010 mg/L _ 

0.012 mg/L [l - (l - 0.4Xl - 0.95)]- 0.4 ■ [l - 0.2]- 0.010 mg/L 


\ 

= 237 gpm 

J 


Q b = (500 gpm)-0.4 (237 gpm)= 405 gpm 

2.2 Pre-Oxidation Processes 

Reduced inorganic As(III) (arsenite) should be converted to As(V) (arsenate) to facilitate removal. 
This step is critical for achieving optimal performance of all unit processes described in this 
Handbook. Conversion to As(V) can be accomplished by providing an oxidizing agent at the head 
of any proposed arsenic removal process. Chlorine, permanganate, ozone, and Filox-R™ 5 are 
highly effective for this purpose. Chlorine dioxide and monochloramine are ineffective in oxidiz¬ 
ing As(III). Ultraviolet (UV) light, by itself, is also ineffective. However, if the water is spiked 
with sulfite, UV photo-oxidation shows promise for As(III) conversion (Ghurye and Clifford, 2001). 
Based on these considerations, only chlorine, permanganate, ozone, and Filox-R™ are discussed 
further in this Handbook. 

Table 2-2 provides a summary of the benefits and drawbacks associated with the use of several 
oxidation technologies. The choice of oxidation method should be based primarily on the arsenic 
treatment technology to be employed (as described in Section 3), and secondarily on factors pro¬ 
vided in Table 2-2. Many small water systems employ chlorine disinfection, either alone or as part 
of a larger treatment process. In most of these instances, the existing chlorination process can be 
optimized to provide concurrent As(III) oxidation. 


5 Filox is a registered trademark of Matt-Son, Inc., Barrington, IL. Filox-R is a trademark of Matt-Son, Inc., 
Barrington, IL. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


18 







Table 2-2. Comparison of Oxidizing Agents. 


Oxidant 


Benefits 


Drawbacks 

Chlorine 

• 

Low relative cost ($0.50/Ib.) 

• 

Formation of disinfection by-products 


• 

Primary disinfection capability 

• 

Membrane fouling 


• 

• 

• 

Secondary disinfectant residual 

MnO, media regenerant 

Oxidizes arsenic in less than 1 minute 

• 

Special handling and storage requirements 

Permanganate 

• 

Unreactive with membranes 

• 

High relative cost ($1.35/Ib.) 


• 

No formation of disinfection by-products 

• 

No primary disinfection capability 


• 

MnO, media regenerant? 

• 

Formation of MnO, particulates 


• 

Oxidizes arsenic in less than 1 minute 

• 

Pink Water 




• 

Difficult to handle 




• 

An additional oxidant may be required for 
secondary disinfection 


Ozone 


No chemical storage or handling required 
Primary disinfection capability 
No chemical by-products left in water 
Oxidizes arsenic in less than 1 minute in 
the absence of interfering reductants 


Sulfide and TOC interfere with conversion and 
increase the required contact time and ozone 
dose for oxidation 

An additional oxidant may be required for 
secondary disinfection 


Solid Phase 
Oxidants 
(Filox Rtm) 


• No chemical storage or handling required 

• No chemical by-products left in water 

• Oxidizes arsenic with an EBCT of 1.5 
minutes in the absence of interfering 
reductants 




Backwashing required 
Backwash waste is generated 
Requires dissolved oxygen to work 
No primary disinfection capability 
An additional oxidant may be required for 
secondary disinfection 

Iron, manganese, sulfide, and TOC increase the 
contact time and dissolved oxygen 
concentration required for oxidation 


2.2.1 Chlorine 

Issues associated with pre-chlorination are: (1) sensitivity of the treatment process to chlo¬ 
rine; (2) disinfection by-product (DBP) formation potential; (3) code requirements associ¬ 
ated with chemical storage and handling; and (4) operator safety. Chlorine can be added 
either as a gas or as liquid hypochlorite, although chlorine gas may not be appropriate for 
small systems. For new chlorine feed installations, these alternatives should be evaluated 
with respect to capital and operating costs, O&M requirements, code restrictions, contain¬ 
ment requirements, footprint, and safety concerns, among other issues. Gas feed is typi¬ 
cally conducted with either 150-pound cylinders or 2,000-pound (1-ton) containers, de¬ 
pending on the rate of chlorine consumption. Small systems normally use the 150-pound 
cylinders. Liquid hypochlorite can either be generated on-site (0.8% strength), or purchased 
as commercial strength (5V* or 12!/ 2 %) liquid hypochlorite. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


19 














The stoichiometric oxidant demand is 0.95 mg of chlorine (as Cl,) per mg of As(III). The 
oxidation-reduction reaction for chlorine (as hypochlorite) is provided in the following equa¬ 
tion. 


H 3 As 0 3 + OC1- H,AsO; + H + + Cf Eqn. 2-7 

The ability of chlorine to convert As(III) to As(V) was found to be relatively independent of 
pH in the range 6.3 - 8.3. Based on laboratory oxidation studies (Ghurye and Clifford, 
2001), chlorine applied in a stoichiometric excess of 3 times was capable of converting over 
95% of As(III) to As(V) within 42 seconds. Dissolved iron, manganese, and total organic 
carbon (TOC) had no significant effects on the conversion time. However, sulfide in 1 and 
2 mg/L concentrations increased the conversion time to 60 seconds. 

The stoichiometric oxidant demands and the oxidation-reduction reactions for chlorine (as 
hypochlorite) to oxidize iron, manganese, and sulfide are provided below. 

Stoichiometric ratio for oxidation of Fe(II) is 0.64 mg Cl, per mg Fe 2+ . 

2Fe 2+ + OC1- + 5H,0 2Fe(OH) 3 + Cf + 4H + Eqn. 2-8 

Stoichiometric ratio for oxidation of Mn(II) is 1.29 mg Cl, per mg Mn 2+ . 

Mn 2+ + OCT + H 2 0 -» MnO, + Cl + 2H + Eqn. 2-9 

Stoichiometric ratio for oxidation of sulfide is 2.21 mg Cl, per mg HS\ 

HS- + OCf S° + CT + OH* Eqn. 2-10 

Information on the design of a chlorination system can be found in Section 5.1, Chlorine 
Pre-Oxidation Design Considerations. 

2.2.2 Permanganate 

Permanganate is a powerful oxidizing agent that is commonly used in iron and manganese 
removal processes. Potassium permanganate exists in solid, granular form and is readily 
soluble in water (60 g/L at room temperature). Most applications involve metering of a 
permanganate solution. 

The stoichiometric oxidant demand is 1.06 mg of permanganate per mg of As(III). The 
oxidation-reduction reaction for permanganate is provided in the following equation. 

3H 3 As 0 3 + 2Mn0 4 " 3H,As0 4 " + H" + 2MnO, + H,0 Eqn. 2-11 

The ability of permanganate to convert As(III) to As(V) was found to be relatively indepen¬ 
dent of pH in the range 6.3 - 8.3. Based on laboratory oxidation studies (Ghurye and 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


20 



Clifford, 2001), permanganate applied in a stoichiometric excess of 3 times was capable of 
converting over 95% of As(III) to As(V) within 36 seconds. Dissolved iron, manganese, 
and TOC had no significant effects on the conversion time. However, sulfide in 1 and 2 
mg/L concentrations increased the conversion time to 54 seconds. 

The stoichiometric oxidant demands and the oxidation-reduction reactions for permangan¬ 
ate to oxidize iron, manganese, and sulfide are provided below. 

Stoichiometric ratio for the oxidation of Fe(II) is 0.71 mg Mn0 4 ' per mg Fe 2+ . 

3Fe 2+ + MnO; + 7H 2 0 -> 3Fe(OH) 3 + MnO, + 5H + Eqn. 2-12 

Stoichiometric ratio for oxidation of Mn(II) is 1.44 mg Mn0 4 ' per mg Mn 2+ . 

3Mn 2+ + 2MnO; + 2H 2 0 -» 5MnO, + 4H + Eqn. 2-13 

Stoichiometric ratio for oxidation of sulfide is 2.48 mg Mn0 4 ' per mg HS\ 

3HS + 2MnO; + 5H + 3S° + 2MnO, + 4H 2 0 Eqn. 2-14 

The use of permanganate has several disadvantages. 

Firstly, it is difficult to handle. It comes as a powder, is very corrosive, and stains nearly 
everything purple. The second drawback is the formation of manganese particulates (MnO,). 
To prevent the accumulation of these deposits in the distribution system, they must be re¬ 
moved via filtration. A third drawback is that, because permanganate is not used as a 
secondary disinfectant, another oxidant may be required for secondary disinfection. Addi¬ 
tionally, if a secondary disinfectant is not used in the distribution system when a POU treat¬ 
ment strategy is implemented, anoxic conditions could develop in the distribution system 
causing the As(V) to reduce back to As(III). This would decrease the effectiveness of the 
POU devices and increase the cost of the treatment. 

Information on the design of a permanganate system can be found in Section 5.2, Perman¬ 
ganate Pre-Oxidation Design Considerations. 

2.2.3 Ozone 

Ozone is the most powerful and rapid-acting oxidizer produced. It is created by exposing 
oxygen, either in air or pure oxygen, to high energy such as an electric discharge field (i.e., 
corona discharge) or to UV radiation. This causes the oxygen molecules to react to form an 
unstable configuration of three oxygen atoms - the oxygen molecule contains only two. 
Because of its instability, ozone is very reactive and is a very efficient oxidant. The only by¬ 
product from oxidation with ozone is oxygen, which is dissolved in aqueous systems. But 
because of ozone’s highly reactive nature, it will quickly self-react and revert back to oxy¬ 
gen if in high concentrations or not used within short periods of time. Therefore, if ozone is 
used as an oxidant, it must be produced on site. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


21 






The stoichiometric oxidant demand is 0.64 mg of ozone per mg of As(III). The oxidation- 
reduction reaction for ozone is provided in the following equation. 

H 3 As0 3 + O, -» H 2 AsO; + H + + 0 2 Eqn. 2-15 

The ability of ozone to convert As(III) to As(V) was found to be relatively independent of 
pH in the range 6.3 - 8.3. Based on laboratory oxidation studies (Ghurye and Clifford, 
2001), ozone applied in a stoichiometric excess of 3 times was capable of converting over 
95% of As(III) to As(V) within 18 seconds. Dissolved iron, manganese, and TOC had no 
significant effects on the conversion time. However, sulfide in 1 and 2 mg/L concentrations 
increased the conversion time to 54 and 132 seconds, respectively. 

The stoichiometric oxidant demands and the oxidation-reduction reactions for ozone to 
oxidize iron, manganese, and sulfide are provided below. 

Stoichiometric ratio for the oxidation of Fe(II) is 0.43 mg 0 3 per mg Fe 2+ . 

2Fe 2+ + 0 3 + 5H 2 0 2Fe(OH) 3 + 0 2 + 4H + Eqn. 2-16 

Stoichiometric ratio for oxidation of Mn(II) is 0.88 mg 0 3 per mg Mn 2+ . 

Mn 2+ + 0 3 + H 2 0 Mn0 2 + 0 2 + 2H + Eqn. 2-17 

Stoichiometric ratio for oxidation of sulfide is 1.50 mg O, per mg HS\ 

HS- + 0 3 + H + -» S° + 0 2 + H 2 0 Eqn. 2-18 

The primary drawback to the use of ozone is that, because ozone does not provide a second¬ 
ary disinfectant, another oxidant may be required for secondary disinfection. Additionally, 
if a secondary disinfectant is not used in the distribution system when a POU treatment 
strategy is implemented, anoxic conditions could develop in the distribution system causing 
the As(V) to reduce back to As(III). This would decrease the effectiveness of the POU 
devices and increase the cost of the treatment. 

Information on the design of an ozonation system can be found in Section 5.3, Ozone Pre- 
Oxidation Design Considerations. 

2.2.4 Solid Phase Oxidants (Filox-R™) 

Filox-R™ is a granular manganese dioxide media that can catalyze the oxidation of As(III) 
to As(V) (Ghurye and Clifford, 2001). This media catalytically oxidizes As(III) to As(V) 
using dissolved oxygen in the water. The Filox-R™ media also tends to adsorb some of the 
arsenic. New media can adsorb as much as 26% of the arsenic. Once the media’s capacity 
is exhausted, the media will no longer remove arsenic but will continue to oxidize it. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


22 



The stoichiometric oxidant demand is 0.21 mg of oxygen per mg of As(III). The oxidation- 
reduction reaction for oxygen is provided in the following equation. 

2H 3 As 0 3 + 0 2(aq) -> 2H 2 As 0 4 - + 2H + Eqn. 2-19 

Based on laboratory oxidation studies (Ghurye and Clifford, 2001) with an empty bed con¬ 
tact time (EBCT) of 1.5 minutes, Filox-R™ was capable of converting over 98.7% of As(III) 
to As(V). Decreasing the pH from 8.3 to 6.0 increased the conversion to 100%. Dissolved 
iron, manganese, hydrogen sulfide, and total organic carbon (TOC) were found to interfere 
with arsenic oxidation when the dissolved oxygen (DO) concentration was low (0.1 mg/L) 
and the EBCT was low (1.5 minutes). Either increasing the DO concentration (to 8.2 mg/L) 
or increasing the EBCT (to 6 minutes), eliminated the effects of these interfering reduc- 
tants. 

Filox-R™ also has the ability to remove iron, manganese, hydrogen sulfide. The stoichio¬ 
metric oxidant demands and the oxidation-reduction reactions for oxygen to oxidize iron, 
manganese, and sulfide are provided below. 

Stoichiometric ratio for the oxidation of Fe(II) is 0.43 mg O, per mg Fe 2+ . 

4Fe 2+ + 30 2 + 6H 2 0 + 2e‘ -» 4Fe(OH) 3 Eqn. 2-20 

Stoichiometric ratio for oxidation of Mn(II) is 0.58 mg 0 2 per mg Mn 2+ . 

Mn 2+ + 0 2 + 2e- -> MnO, Eqn. 2-21 

Stoichiometric ratio for oxidation of sulfide is 0.48 mg O, per mg HS\ 

2HS- + 0 2 + 2H + -> 2S° + 2H 2 0 Eqn. 2-22 

The primary drawback to the use of a solid phase oxidant is that, because the solid phase 
oxidant does not provide a secondary disinfectant, another oxidant may be required for 
secondary disinfection. Additionally, if a secondary disinfectant is not used in the distribu¬ 
tion system when a POU treatment strategy is implemented, anoxic conditions could de¬ 
velop in the distribution system causing the As(V) to reduce back to As(III). This would 
decrease the effectiveness of the POU devices and increase the cost of the treatment. 

Information on the design of a solid phase oxidant system can be found in Section 5.4, Solid 
Phase Oxidant Pre-Oxidation Design Considerations. 

2.3 Sorption Treatment Processes 

The following three forms of sorption treatment are addressed: (1) ion exchange, (2) adsorption to 
AA media, and (3) adsorption on IBS media. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


23 



2.3.1 Ion Exchange 

Ion exchange is a physical-chemical process in which ions are swapped between a solution 
phase and solid resin phase. The solid resin is typically an elastic three-dimensional hydro¬ 
carbon network containing a large number of ionizable groups electrostatically bound to the 
resin. These groups are exchanged for ions of similar charge in solution that have a stronger 
exchange affinity (i.e., selectivity) for the resin. In drinking water treatment, this technol¬ 
ogy is commonly used for POE softening and nitrate removal. 

Arsenic removal is accomplished by continuously passing water under pressure through 
one or more columns packed with exchange resin. Figure 2-8 shows a typical process flow 
diagram for ion exchange. As(V) can be removed through the use of strong-base anion 
exchange resin (SBA) in either chloride or hydroxide form. These resins are insensitive to 
pH in the range 6.5 to 9.0 (USEPA, 2000; reference to Clifford et al., 1998). The following 
paragraphs discuss factors that affect IX system efficiency and economics. 


Raw 

Water 



Treated 

Water 


Backwash Waste Regenerant 

Waste 


Figure 2-8. Ion Exchange Process Flow Diagram. 

The exchange affinity of various ions is a function of the net surface charge. Therefore, the 
efficiency of the IX process for As(V) removal depends strongly on the solution pH and the 
concentration of other anions, most notably sulfates and nitrates. These and other anions 
compete for sites on the exchange resin according to the following selectivity sequence 
(Clifford, 1999). 


SO, 2 ' > HAsO 2 > NO 3 ', CO 2 ' > NO 2 ' > Cl 

4 4 7 3 

High levels of total dissolved solids (TDS) can adversely affect the performance of an IX 
system. In general, the IX process is not an economically viable treatment technology if 
source water contains over 500 mg/L of TDS (Wang et al., 2000) or over 50 mg/L of sulfate 
(S042-) (Kempic, 2002). Figure 2-9 illustrates the effect of sulfate ions on the performance 
of IX media. Although this relationship will not be exactly the same for all waters, it does 
provide a general indication of the impact of sulfates on IX treatment. Additionally, small 
amounts of iron may form a soluble complex with arsenic and carry it out of the column. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


24 

















Figure 2-9. Effect of Sulfate on Ion Exchange Performance (Clifford, 1999). 


One of the primary concerns related to IX treatment is the phenomenon known as chro¬ 
matographic peaking, which can cause As(V) and nitrate levels in the treatment effluent to 
exceed those in the influent stream. This can occur if sulfates are present in the raw water 
and the bed is operated past exhaustion. Because sulfate is preferentially exchanged, in¬ 
coming sulfate anions may displace previously sorbed As(V) and nitrate. In most 
groundwaters, sulfates are present in concentrations that are orders of magnitude greater 
than As(V). Therefore, the level of sulfates is one of the most critical factors to consider for 
determining the number of bed volumes that can be treated. A useful technique for avoid¬ 
ing chromatographic peaking is to perform careful monitoring of the effluent stream during 
startup. Then, based on the analysis, determine a setpoint for the total volume treated be¬ 
fore breakthrough occurs. This volumetric setpoint would then be used to trigger the regen¬ 
eration cycle. Regular monitoring of the column effluent should be continued to insure that 
loss of capacity in the media does not lead to premature breakthrough. Frequently, the 
volumetric setpoint is based on the breakthrough of sulfate. The kinetics of breakthrough 
are rapid; therefore a margin of safety should be provided or a guard column should be used 
in series with the IX column. 

Hydraulic considerations associated with IX include empty bed contact time (EBCT) and 
headloss. The recommended EBCT range is 15 minutes. EBCTs as low as 1.5 minutes 
have been shown to work in some installations. The presence of suspended solids in the 
feed water could gradually plug the media, thereby increasing headloss and necessitating 
more frequent backwashing. Therefore, pre-filtration is recommended if the source water 
turbidity exceeds 0.3 NTU. 

Another concern is resin fouling. Resin fouling occurs when mica or mineral-scale coat the 
resin or when ions bond the active sites and are not removable by the standard regeneration 
methods. This can have a significant effect on the resins capacity as the media becomes 
older. Replacement of the media or reconditioning may be needed after a number of years. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


25 














Resin that has been used to exhaustion can be regenerated on-site using a four-step process: 
(1) backwash, (2) regeneration with brine (for chloride-form SB A) or caustic soda (for 
hydroxide-form SBA), (3) slow water rinse, and (4) fast water rinse. It is recommended that 
small systems use the chloride-form resin due to the easier chemical handling consider¬ 
ations for regeneration. 

Single-pass regeneration of anion exchange media typically produces 45 bed volumes of 
brine waste (USEPA, 2000; reference to AwwaRF, 1998). In a study conducted by the 
USEPA (Wang et al., 2000), dissolved arsenic concentrations in spent brine ranged from 
1.83 mg/L to 38.5 mg/L, with an average value of 16.5 mg/L. It is anticipated that for most 
sources with arsenic levels above 0.010 mg/L and sulfate levels below 50 mg/L, the spent 
regenerant will contain at least 5.0 mg/L of dissolved arsenic. 

Liquid waste streams (less than 0.5% solids) are evaluated directly against the TC to charac¬ 
terize hazard potential. Those liquid waste streams that contain more than 5.0 mg/L of 
arsenic would be classified as hazardous waste based on TC. 

Indirect discharge may be an option since wastes that pass through a sewer system to a 
POTW are exempt from RCRA regulation. The critical factor dictating the feasibility of 
this option will be TBLLs for arsenic and TDS. The background level will change because 
of the drinking water treatment process, which may lead to revised TBLLs. The revised 
TBLL would be used to determine if the liquid waste stream could be discharged to the 
POTW. Water systems that elect to use brine recycle will further concentrate the dissolved 
arsenic and solids, making it even more unlikely that the stream will meet local TBLLs. 

Because of RCRA requirements and cost implications, off-site disposal of hazardous waste 
or on-site treatment of waste is likely to be infeasible for small water systems. 

Replacement of IX media may be required over time. Based on previous studies, spent IX 
resin does not exceed any TC concentrations, enabling it to be disposed of in a municipal 
solid waste landfill. This is true regardless of whether or not the media has been regener¬ 
ated prior to conducting the TCLP 

Information on the design of an IX system can be found in Section 6, Process Design Con¬ 
siderations. 

2.3.2 Activated Alumina 

Activated alumina is a porous, granular material with ion exchange properties. The media, 
aluminum trioxide, is prepared through the dehydration of aluminum hydroxide at high 
temperatures. AA grains have a typical diameter of 0.3 to 0.6 mm and a high surface area 
for sorption. 

In drinking water treatment, packed-bed AA adsorption is commonly used for removal of 
natural organic matter and fluoride. The removal of As(V) by AA adsorption can be accom- 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


26 



plished by continuously passing water under pressure through one or more beds packed 
with AA media. Figure 2-10 shows a typical process flow diagram for ion exchange. Dashed 
lines and boxes indicate optional streams and processes. The efficiency and economics of 
the system are contingent upon several factors, as discussed in the following paragraphs. 


Oxidant - 


Acid-, 


Base-i 


Raw 

Water 


Pre- 


pH 


Pre- 


Activated 


pH 

Oxidation 


Adjustment 


Filtration 

- T - 

► 

Alumina 


Re-Adjustment 


* 

Backwash 

Waste 


▼ 

Waste 


Regenerant 


Treated 

Water 


Figure 2-10. Activated Alumina Process Flow Diagram. 


The level of competing ions affects the performance of AA for As(V) removal, although not 
in the same manner nor to the same extent as IX. The following selectivity sequence has 
been established for AA adsorption (USEPA, 2000): 


OH > H 2 AsO; > Si(OH) 3 0 > F > HSe0 3 > TOC > S0 4 2 ' > H,As0 3 

The selectivity of AA towards As(III) is poor, owing to the overall neutral molecular charge 
at pH levels below 9.2. Therefore, pre-oxidation of As(III) to As(V) is critical. Several 
different studies have established the optimum pH range as 5.5-6.0, and demonstrated greater 
than 98% arsenic removal under these conditions. AA column runs operated under acidic 
pH conditions are 5 to 20 times longer than under natural pH conditions (6.0-9.0), as de¬ 
picted in Figure 2-11. However, many small utilities elect to conduct AA treatment under 
natural pH conditions. In these cases, the savings in capital and chemical costs required for 
pH adjustment and media regeneration offset the costs associated with decreased run length. 



Water pH 

Figure 2-11. Effect of pH on Activated Alumina Performance 
(USEPA, 2000; original data from Hathaway and Rubel, 1987). 


Arsenic Treatment Technology’ Evaluation Handbook for Small Systems 


27 



























Several constituents can interfere with the adsorption process, either by competing for ad¬ 
sorption sites or clogging the media with particulate matter. These constituents, and their 
corresponding problematic levels, are summarized in Table 2-3. 


Table 2-3. Water Quality Interferences with AA Adsorption. 


Parameter 

Problem Level 

Chloride 

250 mg/L 1 

Fluoride 

2 mg/L 1 

Silica 

30 mg/L 2 

Iron 

0.5 mg/L 1 

Manganese 

0.05 mgT 1 

Sulfate 

720 mg/L 3 

Dissolved Organic Carbon 

4 mg/L 3 

Total Dissolved Solids 

1,000 mgT 3 


1 AwwaRF (2002) 

2 Clifford (2001) 

3 Wang, et aL (2000) 


Hydraulic considerations associated with AA adsorption include empty bed contact time 
and headloss. For most types of AA media, the recommended EBCT range is 310 minutes. 
The presence of suspended solids in the feed water could gradually clog the media, thereby 
increasing headloss. Pre-filtration is recommended for sources where the turbidity exceeds 
0.3 NTU. 

The technologies and market for alumina-based adsorptive media continue to expand. There 
are several emerging proprietary media, commonly referred to as modified AA, which con¬ 
tain alumina in a mixture with other substances such as iron and sulfur. In some instances, 
these media have greater overall adsorptive capacities, enhanced selectivity towards ar¬ 
senic, and/or greater overall operational flexibility than conventional AA, thus making them 
more cost-effective. To account for this industry growth, the decision trees in Section 3 
include a treatment alternative known as modified-AA. If this endpoint is reached, the 
water system should strongly consider more detailed investigation into current, innovative 
media. It is required by most states that all media used in water treatment be approved 
under NSF Standard 61. 

AA media can either be regenerated on-site or disposed of and replaced with fresh media. 
On-site regeneration of AA media typically produces 37 to 47 bed volumes of caustic soda 
waste (USEPA, 2000). Because of the high pH of the regeneration process, roughly 2% of 
the AA media dissolves during each regeneration sequence. Therefore, the waste solution 
typically contains high levels of TDS, aluminum, and soluble arsenic. In most cases, this 
arsenic level will exceed the 5.0 mg/L TC, and the waste stream will be classified as a 
hazardous liquid waste. Backwashing may also be necessary to prevent cementation of the 
media, which can occur as a result of dissolution caused by chemical addition during regen¬ 
eration. For these reasons, regeneration of AA is likely to be an infeasible option for most 
small water systems. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


28 















The alternative for utilities considering AA adsorption is the use of throwaway media, oper¬ 
ated with or without pH adjustment. The savings in O&M requirements and residuals dis¬ 
posal may offset the cost of periodically replacing the media. For this option, systems must 
provide an equalization basin for backwash water (if applicable) and a staging area to store 
spent media prior to disposal. Throwaway AA media is expected to not exceed any TCs, 
enabling it to be disposed of in a municipal solid waste landfill (Wang et al., 2000). As an 
added convenience to small systems, media suppliers may offer a media disposal service 
with the purchase of their media. 

Information on the design of an AA system can be found in Section 6, Sorption Process 
Design Considerations. Information on POU systems can be found in Section 8.1.1, 
Adsoprtion Point-of-Use Treatment. 

2.3.3 Iron Based Sorbents 

Adsorption on IBS is an emerging treatment technique for arsenic. Examples of IBS prod¬ 
ucts currently available with NSF 61 approval are shown in Table 2-4. The sorption process 
has been described as chemisorption (Selvin et al., 2000), which is typically considered to 
be irreversible. It can be applied in fixed bed pressure columns, similar to those for AA. 
Due to limited performance research at the time the Arsenic Rule was promulgated, it was 
not designated as a BAT or a SSCT by the USEPA. 


Table 2-4. Examples of Iron Based Sorbents. 1 


Product Name 

Company 

Material Type 

G2 

ADI International 

Modified Iron 

SMI III 

SMI 

Iron/Sulfur 

GFH 

U.S. Filter/General Filter Products 

Granular Ferric Hydroxide 

Bayoxide E 33 

Bayer AG 

Iron Oxide 

1 Examples are taken from Rubel 2003. 


The few studies conducted with IBS media have revealed that the affinity of this media for 
arsenic is strong under natural pH conditions, relative to AA. This feature allows IBS to 
treat much higher bed volumes without the need for pH adjustment. However, similar to 
AA, optimal IBS performance is obtained at lower pH values. The recommended operating 
conditions include an EBCT of 5 minutes and a hydraulic loading rate of 5 gpm/sft. 

Phosphate has been shown to compete aggressively with As(V) for adsorption sites. Each 
0.5 mg/L increase in phosphate above 0.2 mg/L will reduce adsorption capacity by roughly 
30% (Tumalo, 2002). 

In previous studies, exhausted IBS media has not exceeded any TCs, enabling it to be dis¬ 
posed of in a municipal solid waste landfill (MacPhee et al., 2001). As an added conve¬ 
nience to small systems, media suppliers may offer a media disposal service with the pur¬ 
chase of their media. 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


29 











Information on the design of IBS systems can be found in Section 6, Sorption Process 
Design Considerations. Information on POU systems can be found in Section 8.1.1, Ad¬ 
sorption Point-of-Use Treatment. 

2.4 Membrane Treatment Processes 

Membrane separation technologies are attractive arsenic treatment processes for small water sys¬ 
tems. They can address numerous water quality problems while maintaining simplicity and ease of 
operation. The molecular weight cut-off of microfiltration (MF) processes necessitates the use of a 
coagulation stage to generate arsenic-laden floe and is therefore discussed in Section 2.5.3, Coagu¬ 
lation-Assisted Microfiltration. However, RO units have a much larger retention spectrum, and can 
be used as stand-alone arsenic treatment under most water quality conditions. Figure 2-12 provides 
a block flow diagram for a typical RO membrane process. Dashed lines indicate optional streams 
and processes. 



Treated 

Water 


Backwash 

Waste 


Retentate 

Waste 


Figure 2-12. RO Membrane Process Flow Diagram. 

Most RO membranes are made of cellulose acetate or polyamide composites cast into a thin film. 
The semi-permeable (non-porous) membrane is then constructed into a cartridge called an RO 
module, typically either hollow-fiber or spiral-wound. 

RO is a pressure-driven membrane separation process capable of removing dissolved solutes from 
water by means of particle size, dielectric characteristics, and hydrophilicity/hydrophobicity. Re¬ 
verse osmosis is capable of achieving over 97% removal of As(V) and 92% removal of As(III) in a 
single pass (NSF, 2001a; NSF 2001b). As an added benefit, RO also effectively removes several 
other constituents from water, including organic carbon, salts, dissolved minerals, and color. The 
treatment process is relatively insensitive to pH. In order to drive water across the membrane 
surface against natural osmotic pressure, feed water must be sufficiently pressurized with a booster 
pump. For drinking water treatment, typical operating pressures are between 100 and 350 psi. 
Water recovery is typically 60 -80%, depending on the desired purity of the treated water. In some 
cases, particularly POU applications, RO units are operated at tap water pressures. This results in 
a significantly lower water recovery. 

Multiple RO units can be applied in series to improve the overall arsenic removal efficiency. Fig¬ 
ure 2-13 illustrates a 2-stage RO treatment process. The overall rejection rate for a multi-staged 
RO treatment process can be calculated as: 


Arsenic Treatment Technology’ Evaluation Handbook for Small Systems 


30 












Eqn. 2-23 


Where: 

E = 



n = 


E = 1 — (1 — E s ) n 

Overall Rejection Rate (Treatment Efficiency), 
Individual Stage Contaminant Rejection Rate, and 
Number of Stages. 


Stage 1 


Stage 2 


Feed 

Water 



Permeate 

Combined 

Retentate 


Figure 2-13. Two-Stage RO Treatment Process Schematic. 


Membrane fouling can occur in the presence of NOM and various inorganic ions, most notably 
calcium, magnesium, silica, sulfate, chloride, and carbonate. These ions can be concentrated (in 
the retentate) to concentrations an order of magnitude higher than in raw water. This can lead to the 
formation of scale on the membrane surface, which in turn can cause a decline in arsenic rejection 
and water recovery. Further, the membrane surface can act as a substrate for biological growth. 
Membrane cleaning can restore treatment performance; however, the cleaning process is difficult 
and costly. The rate of membrane fouling depends on the configuration of the module and feed 
water quality. Most RO modules are designed for cross-flow filtration, which allows water to 
permeate the membrane while the retentate flow sweeps rejected salts away from the membrane 
surface. In many cases, pre-filtration (commonly through sand or granular activated carbon) is 
worthwhile. This minimizes the loading of salt precipitates and suspended solids on the membrane 
surface, thereby extending run length, improving system hydraulics, and reducing O&M require¬ 
ments. 


Some membranes, particularly those composed of polyamides, are sensitive to chlorine. Feed wa¬ 
ter should be dechlorinated (if applicable) in these instances. Another potential concern associated 
with RO treatment is the removal of alkalinity from water, which in turn could affect corrosion 
control within the distribution system. If feasible, this problem can usually be avoided by conduct¬ 
ing sidestream treatment for arsenic removal. 

Indirect discharge to a POTW or direct discharge to an on-site sewerage system (for POU systems) 
are considered the most viable residuals disposal option. For those systems considering indirect 
discharge, the retentate must meet local TBLLs for arsenic. The arsenic concentration in the retentate 
can be calculated using Equation 2-24. 


r C '- E s 

Ri 1-p 

Where: 

C R j = Concentration of Species i in the Retentate (mg/L), 

C, = Concentration of Species i in the Feed Stream (mg/L), 


Eqn. 2-24 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


31 











E s = Individual Stage Contaminant Rejection Rate (% expressed as a decimal), and 
(3 = Individual Stage Water Recovery Rate (% expressed as a decimal). 

It is not anticipated that a small system will use an RO system for centralized treatment because RO 
systems for centralized treatment can be expensive. Therefore, no design information on central¬ 
ized systems has been provided in this Handbook. However, information on RO POU systems can 
be found in Section 8.1.2, Reverse Osmosis Point-of-Use Treatment. 

2.5 Precipitation/Filtration Treatment Processes 


• The following four chemical precipitation processes are addressed: 

• LS, 

• Conventional Gravity Coagulation/Filtration, 

• CMF, 

• CADF, and 

• Oxidation/Filtration. 

Figure 2-14 provides a block flow diagram for a generic precipitation/filtration process. Dashed 
lines and boxes indicate optional streams and processes. 


Raw 

Water 



Acid/Base 



Backwash 

Waste 


Treated 

Water 


Figure 2-14. Generic Precipitation/Filtration Process Flow Diagram. 

2.5.1 Enhanced Lime Softening 

Fime softening is a chemical-physical treatment process used to remove calcium and mag¬ 
nesium cations from solution. The addition of lime increases the pH of solution, thereby 
causing a shift in the carbonate equilibrium and the formation of calcium carbonate and 
magnesium hydroxide precipitates. These precipitates are amenable to removal by clarifi¬ 
cation and filtration. 

LS solely for arsenic removal is uneconomical and is generally considered cost-prohibitive. 
However, for water systems that use LS to reduce hardness, the process can be enhanced for 
arsenic removal. To remove As(V), additional lime is added to increase the pH above 10.5. 
In this range magnesium hydroxide precipitates and As(V) is removed by co-precipitation 
with it. As(V) removal by co-precipitation with calcium carbonate (i.e., below a pH of 
10.5) is poor (less than 10%). 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


32 














The amount of waste residual produced by LS is dependent on the hardness removed. While 
the total volume of waste produced from LS is typically higher than that produced by coagu¬ 
lation/filtration and co-precipitative processes, the arsenic concentration in the sludge is 
generally lower because more solids are produced. Typical solids concentrations are 1 - 4% 
arsenic. Prior to disposal, this waste residual will require thickening and dewatering, most 
likely via mechanical devices. Previous studies have indicated that typical lime sludge will 
not exceed TC limits, enabling it to be disposed of in a municipal solid waste landfill (Fields 
et al., 2000a). 

Because LS is unlikely to be installed solely for arsenic removal in small systems, no design 
discussion is provided in this Handbook. 

2.5.2 Conventional Gravity Coagulation/Filtration 

Coagulation is the process of destabilizing the surface charges of colloidal and suspended 
matter to allow for the agglomeration of particles. This process results in the formation of 
large, dense floe, which is amenable to removal by clarification or filtration. The most 
widely used coagulants for water treatment are aluminum and ferric salts, which hydrolyze 
to form aluminum and iron hydroxide particulates, respectively. 

Conventional gravity coagulation/filtration processes use gravity to push water through a 
vertical bed of granular media that retains the floe and are typically used within surface 
water treatment plants. They are less commonly used for treatment of groundwater supplies 
since these sources usually contain much lower concentrations of suspended solids, organic 
carbon, and pathogenic microorganisms. Installation and operation of a conventional grav¬ 
ity coagulation/filtration process solely for arsenic removal is uneconomical. 

Coagulation/filtration processes can be optimized to remove dissolved inorganic As(V) from 
water. The mechanism involves the adsorption of As(V) to an aluminum or ferric hydrox¬ 
ide precipitate. The As(V) becomes entrapped as the particle continues to agglomerate. 
As(III) is not effectively removed because of its overall neutral charge under natural pH 
conditions. Therefore, pre-oxidation is recommended. The efficiency and economics of 
the system are contingent upon several factors, including the type and dosage of coagulant, 
mixing intensity, and pH. In general, however, optimized coagulation-filtration systems are 
capable of achieving over 90% removal of As(V) and producing water with less than 0.005 
mg/L of As(V). Influent As(V) levels do not appear to impact the effectiveness of this 
treatment process. 

Iron-based coagulants, including ferric sulfate and ferric chloride, are more effective at 
removing As(V) than their aluminum-based counterparts. This is because iron hydroxides 
are more stable than aluminum hydroxides in the pH range 5.5 to 8.5. A fraction of the 
aluminum remains as a soluble complex, which is incapable of adsorbing As(V) and can 
pass through the filtration stage. The optimal pH ranges for coagulation with aluminum and 
ferric salts are 5 to 7 and 5 to 8, respectively. At pH values above 7, the removal perfor¬ 
mance of aluminum-based coagulants drops markedly. Feed water pH should be adjusted 


Arsenic Treatment Technology’ Evaluation Handbook for Small Systems 


33 



to the appropriate range prior to coagulant addition. Post-filtration pH adjustment may be 
necessary to optimize corrosion control and comply with other regulatory requirements. 

Several batch studies have demonstrated that As(V) removal is positively related to coagu¬ 
lant dosage. However, specific dose requirements needed to meet As(V) removal objec¬ 
tives were contingent upon the source water quality and pH. Effective coagulant dosage 
ranges were 5-25 mg/L of ferric chloride and as much as 40 mg/L of alum. 

Water intended for indirect discharge will be subject to TBLLs for TDS and arsenic. Dewa¬ 
tering can be accomplished by gravity thickening, followed by other mechanical or non¬ 
mechanical techniques. Settling basins can be used to allow settleable solids to drop out of 
solution via gravity, while the supernatant can be decanted and recycled to the process head. 
The solids can be slurried out periodically and passed through a small filter press for dewa¬ 
tering. The resultant sludge can be disposed of in a municipal solid waste landfill if it meets 
the criteria of the PFLT (no free liquid) and the TCLP. Previous studies have indicated that 
typical coagulation/filtration sludge will not exceed TC limits (Fields et al., 2000a). 

Because conventional gravity coagulation filtration is unlikely to be installed solely for 
arsenic removal in small systems, no design discussion is provided in this Handbook. 

2.5.3 Coagulation-Assisted Microfiltration 

Coagulation-Assisted Microfiltration uses the same coagulation process described above. 
However, instead of the granular media filtration step, the water is forced through a semi- 
permeable membrane by a pressure differential. The membrane retains the As(V) laden 
floe formed in the coagulation step. 

The use of pre-engineered CMF package plants is a realistic possibility for new installations 
where water quality precludes the use of sorption treatment. Due to limited full-scale appli¬ 
cation, it was not designated as a BAT by the USEPA but was listed as a SSCT in the final 
rule. 

The membrane must be periodically backwashed to dislodge solids and restore hydraulic 
capacity. Backwash water is typically a high-volume, low solids (less than 1.0%) waste 
stream. The specific amount of solids will depend on several factors, including coagulant 
type, dosage, filter run length, and ambient solids concentration. Two treatment options are 
available for this waste stream: (1) indirect discharge, and (2) dewatering and sludge dis¬ 
posal (AwwaRF 2000). 

Water intended for indirect discharge will be subject to TBLLs for TDS and arsenic. Dewa¬ 
tering can be accomplished by gravity thickening, followed by other mechanical or non¬ 
mechanical techniques. Settling basins can be used to allow settleable solids to drop out of 
solution via gravity, while the supernatant can be decanted and recycled to the process head. 
The solids can be slurried out periodically and passed through a small filter press for dewa¬ 
tering. The resultant sludge can be disposed of in a municipal solid waste landfill if it meets 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


34 



the criteria of the PFLT (no free liquid) and the TCLP. Previous studies have indicated that 
typical CMF sludge will not exceed TC limits (Fields et al., 2000a). 

Design of a CADF system can be found in Section 7, Pressurized Media Filtration Process 
Design Considerations. 

2.5.5 Oxidation/Filtration 

Oxidation/filtration refers to processes that are designed to remove naturally occurring iron 
and manganese from water. The processes involve the oxidation of the soluble forms of 
iron and manganese to their insoluble forms and then removal by filtration. If arsenic is 
present in the water, it can be removed via two primary mechanisms: adsorption and co¬ 
precipitation. First, soluble iron and As(III) are oxidized. The As(V) then adsorbs onto the 
iron hydroxide precipitates that are ultimately filtered out of solution. 

Although some arsenic may be removed by adsorption/co-precipitation with manganese, 
iron is much more efficient for arsenic removal. The arsenic removal efficiency is strongly 
dependent on the initial iron concentration and the ratio of iron to arsenic. In general, the 
Fe:As mass ratio should be at least 20:1. These conditions customarily result in an arsenic 
removal efficiency of 80-95%. In some cases, it may be appropriate to add ferric coagulant 
to the beginning of the iron removal process to optimize arsenic removal. 

The effectiveness of arsenic co-precipitation with iron is relatively independent of source 
water pH in the range 5.5 to 8.5. However, high levels of NOM, orthophosphates, and 
silicates weaken arsenic removal efficiency by competing for sorption sites on iron hydrox¬ 
ide precipitates (Fields et al., 2000b). 

The common iron/manganese methods consist of (1) air oxidation or chemical oxidation 
followed by media filtration and (2) potassium permanganate oxidation followed by a green¬ 
sand media filter. The latter process is commonly referred to as the greensand process. The 
greensand process can be operated on an intermittent regeneration (IR) basis or on a con¬ 
tinuous feed (CF) basis. With IR operational procedure, the greensand filter is periodically 
regenerated with potassium permanganate following the back washing of the filter. In the 
CF mode, permanganate or chlorine is continuously added to the feed water ahead of green¬ 
sand filter. 

In the air/chemical oxidation filtration iron removal process, the iron is oxidized with either 
air (aeration tower) or with an oxidizing chemical, usually chlorine. Because of the limita¬ 
tions of air to oxidize As(III), chlorine is normally used in order for the process to be effec¬ 
tive for arsenic removal. After the water is oxidized, it is filtered with a granular media to 
remove the iron hydroxide precipitates that contain the adsorbed arsenic. The effectiveness 
of the granular media is important because any iron particles that manage to get through the 
filter media will contain some arsenic. 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


35 





The greensand process is a special case of pressurized granular-media filtration where the 
granular media, greensand, catalyzes the oxidation and precipitation of iron and manga¬ 
nese. In the greensand process, operated an IR basis, the water is passed through a column 
of greensand media, which adsorbs and catalyzes the oxidation of the iron and manganese. 
In order for greensand to retain its adsorption and catalytic oxidation capabilities, the media 
must be regenerated with permanganate or chlorine. When operated on an IR basis, the 
greensand filter column is taken offline and the media is soaked in a solution of permanga¬ 
nate. In the CF mode, permanganate or chlorine is continuously added to the feed water 
ahead of greensand filter where they provide continuous oxidation of the iron and As(III) 
and regeneration of the greensand. If the arsenic in the ground water is not already oxidized 
to As(V), it is recommended that CF process using chlorine or permanganate be used to 
provide continuous oxidation of the iron, manganese, and As(III). 

Greensand is manufactured by coating glauconite with manganese dioxide. Other manga¬ 
nese dioxide media are also used for iron and manganese removal such as pyrolucite, 
Pyrolox® 6 , Filox-R™ 7 , MTM® 8 , BIRM® 9 , and Anthrasand. Greensand and some of the 
other manganese dioxide media (Filox-R™) have been shown to have some arsenic adsorp¬ 
tive effectiveness in removing arsenic from drinking water (Hanson et al., 1999, Fields et 
al., 2000b, Ghurye and Clifford, 2001). 

In all oxidation/filtration processes, the filter media must be periodically backwashed to 
dislodge solids and restore hydraulic capacity. Backwash water is typically a high-volume, 
low solids (less than 0.1%) waste stream. The specific amount of solids will depend on 
several factors, including raw water iron levels, coagulant addition (if any), filter run length, 
and background solids concentration. Two treatment options are available for this waste 
stream: (1) indirect discharge and (2) dewatering and sludge disposal. 

Water intended for indirect discharge will be subject to TBLLs for TDS and arsenic. The 
background level will change because of the drinking water treatment process, which may 
lead to revised TBLLs. The revised TBLL would be used to determine if the liquid waste 
stream could be discharged to the POTW. Dewatering can be accomplished by gravity 
thickening, followed by other mechanical or non-mechanical techniques. Settling basins 
can be used to provide gravity clarification, while the supernatant can be decanted and 
recycled to the process head. The solids can be slurried out periodically and passed through 
a filter press for dewatering. The resultant sludge can be disposed of in a municipal solid 
waste landfill if it passes the PFLT (no free liquid) and the TCLP. Previous studies have 
indicated that typical ferric coagulation-filtration sludge will not exceed TC limits (Fields 
et al., 2000b). 

Design of an oxidation/filtration system can be found in Section 7, Pressurized Media Fil- 

6 Pyrolox is a trademark of American Materials. 

7 Filox is a registered trademark of Matt-Son, Inc., Barrington, IL. Filox-R is a trademark of Matt-Son, Inc., 
Barrington, IL. 

8 MTM is a registered trademark of Clack Corporation, Windsor, WI. 

9 Birm is a registered trademark of Clack Corporation, Windsor, WI. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


36 




tration Process Design Considerations. 

2.6 Point-of-Use Treatment 

Under the final Arsenic Rule, POU devices are approved as SSCTs. However, SDWA requires that 
the devices be owned, controlled, and maintained by the public water utility or by an agency under 
contract with the water utility. Therefore, the responsibility of operating and maintaining the de¬ 
vices cannot be passed to the customer. 

POU devices are particularly attractive for removing contaminants that pose only an ingestion risk, 
as is the case with arsenic. This is because a very small fraction of the total water supplied to a 
given household is ultimately consumed. In most cases, the POU unit is plumbed in at the kitchen 
sink (the device will have its own faucet). 

The primary advantage of employing POU treatment in a small system is reduced capital and treat¬ 
ment costs, relative to centralized treatment. On the downside, however, these programs generally 
incur higher administrative and monitoring costs to make sure that all units are functioning prop¬ 
erly. Previous studies have suggested that POU programs are an economically viable alternative to 
centralized treatment for systems serving roughly 50-500 people. 

Most POU devices do not address the issue of pre-oxidation. While RO may remove As(III) to 
acceptable standards, sorptive processes such as AA or IBS will probably not. In this case, water 
systems may need to conduct centralized chlorine treatment to convert As(III) to As(V). There is 
also a concern that even with centralized pre-oxidation, anoxic conditions could exist in the distri¬ 
bution system that allow As(V) to reduce back to As(III). Depending on the extent of reduction, 
this could be detrimental to a POU program. 

The technologies that are most amenable to POU treatment include AA, IBS, and RO. AA and RO 
are approved as SSCTs for POU applications (USEPA, 2002a). Although there are no IBS systems 
currently approved as SSCTs, there are several media currently being tested. 

The primary criteria for selecting an appropriate POU treatment device are arsenic removal perfor¬ 
mance and cost. The unit must be independently certified against NSF/ANSI product standards to 
be used for compliance purposes. 

More information on POU technologies and can be found in Section 8, Point-of-Use Treatment , 
and in USEPA’s soon to be released Guidance for Implementing a Point-of-Use or Point-of-Entry 
Treatment Strategy for Compliance with the Safe Drinking Water Act (USEPA, 2002b Draft). 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


37 









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Arsenic Treatment Technology Evaluation Handbook for Small Systems 


38 



Section 3 

Arsenic Treatment Selection 


3.1 Selection Criteria 

The task of navigating through the alternative arsenic treatment technologies involves several 
technical considerations. Although nearly all of the unit processes previously presented could be 
used for arsenic reduction at an arbitrary site, some are more economically viable under specific 
circumstances. Optimization of existing processes is a realistic option for some utilities. Although 
most water systems today have been designed without the goal of arsenic removal, many current 
practices may accomplish incidental removal. Optimization of these processes is a realistic option. 
The utility should coordinate the selection and implementation process with its state drinking water 
program. 

3.1.1 Source Water Quality 

Source water quality dictates the performance of the removal processes identified in Section 
2. In turn, process performance, associated O&M requirements, and residuals disposal 
dictate the economics of a particular treatment approach. Therefore, it is important that 
utilities conduct thorough up-front monitoring of water quality at all active sources to make 
the most informed treatment selection decision. 

Tables 3-1 and 3-2 provide a summary of recommended monitoring parameters and associated 
analytical methods. The parameters are divided into two categories: (1) Key and (2) Other. 
Key parameters are those most critical to evaluating the treatment performance potential of 
various arsenic removal processes. These parameters should be monitored multiple times 
over the course of several weeks or months to capture variability in concentrations. Other 
parameters should be monitored at least once in order to optimize the selected arsenic 
treatment method. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


39 












Table 3-1. Key Water Quality Parameters to be Monitored. 


Parameter 

USEPA Method 

Standard Method 3 

ASTM 4 

Arsenic, Total 1 

200.8 

200.9 

3113 B 

3114 B 

D2972-93B 

D2972-93C 

Arsenite {As(III)} 


3500-As B 


Arsenate {As(V)} 


3500-AsB 


Chloride (CT) 2 

300.0 

4110 B 
4500-C1D 
4500-C1 B 

D4327-91 

D512-89B 



4110 B 


Fluoride (F') 1,2 

300.0 

4500-F" B 
4500-F- C 
4500-F’ D 

4500-F- E 

D4327-91 

D1179-93B 


200.7 

200.9 

3120 B 


Iron (Fe) 2 

3111 B 

3113 B 



200.7 

3120 B 


Manganese (Mn) 2 

200.8 

3111 B 



200.9 

3113 B 


Nitrate (NO, ) 1 

300.0 

353.2 

4110 B 
4500-NO; F 
4500-NO; D 
4500-NO; E 

D4327-91 

D3867-90A 

D3867-90B 

Nitrite (NO;) 1 

300.0 

353.2 

4110 B 
4500-NO; F 
4500-NO; E 
4500-NO; B 

D4327-91 

D3867-90A 

D3867-90B 


365.1 

300.0 

4500-P F 

D515-88A 

D4327-91 

Orthophosphate (PO; 3 ) 1 

4500-P E 

4110 B 

pH 1 - 2 

150.1 

150.2 

4500-PT B 

D1293-95 



4500-Si D 


Silica 1 

200.7 

4500-Si E 
4500-Si F 

D859-95 



4110 B 


Sulfate (SO; 2 ) 2 

300.0 

375.2 

4500-SO/- F 

4500-S0 4 2 - C 
4500-SO/' D 
4500-SO 2 ' E 

D4327-91 

D516-90 

Total Dissolved Solids (TDS) 2 


2540 C 


Total Organic Carbon (TOC) 

415.1 




1 USEPA Approved Methods for Drinking Water Analysis of Inorganic Chemicals and other parameters. 

2 USEPA Recommended Methods for Secondary Drinking Water Contaminants. 

3 18th and 19th editions of Standard Methods for the Examination of Water and Wastewater, 1992 and 1995, 
American Water Works Association (AWWA). 

4 Annual Book of ASTM Standards, 1994 and 1996, Vols. 11.01 and 11.02, American Society for Testing 
and Materials (ASTM). 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


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Table 3-2. Other Water Quality Parameters to be Monitored. 


Parameter 

USEPA Method 

Standard Method 3 

ASTM 4 

Alkalinity 1 


2320 B 

D1067-92B 


200.7 

3120 B 


Aluminum (Al) 2 

200.8 

3113 B 



200.9 

3111 D 


Calcium (Ca +2 ) 1 

200.7 

3500-Ca D 

3111 B 

3120 B 

D511-93A 

D511-93B 

Magnesium (Mg +2 ) 1 

200.7 

3113 B 

3120 B 
3500-Mg E 

D511-53B 

D511-93B 

Turbidity 

180.1 



Water Hardness 

215.1 

242.1 




1 USEPA Approved Methods for Drinking Water Analysis of Inorganic Chemicals and other parameters. 

2 USEPA Recommended Methods for Secondary Drinking Water Contaminants. 

3 18th and 19th editions of Standard Methods for the Examination of Water and Wastewater, 1992 and 1995, 
American Water Works Association (AWWA). 

4 Annual Book of ASTM Standards, 1994 and 1996, Vols. 11.01 and 11.02, American Society for Testing 
and Materials (ASTM). 


3.1.2 Process Evaluation Basis 

There are several variables, design criteria, and assumptions that should be established prior 
to navigating the decision trees and cost tables. These include the following: 

• Existing Treatment Processes 

• Target Finished Water Arsenic Concentration 

• TBLLs for Arsenic and TDS 

• Domestic Waste Discharge Method 

• Land Availability 

• Labor Commitment 

• Acceptable Percent Water Loss 

• Maximum Source Flowrate 

• Average Source Flowrate 

• State or primacy agency requirements that are more stringent than those of the USEPA. 

3.2 Process Selection Decision Trees 


Decision trees are useful tools for narrowing the field of available treatment technologies to those 
that are most economical for a particular system. This is accomplished through a series of input- 
output blocks, which direct the utility along the path towards the best technologies. While they do 
not always point to a single solution, they allow the utility to rapidly eliminate some technologies 
that are cost-prohibitive for a specific application. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


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It is critical that the utility employ these decision trees, rather than the cost correlation curves, 
as the primary tool for selecting an arsenic mitigation strategy. These trees take into account 
system-specific conditions and system preferences. 

The decision trees guide the utility to the technologies that are expected to work best for their 
particular situation. In some cases, the pathway is contingent upon a water utility’s willingness to 
impose a particular change in their operating scheme. These decision-making scenarios were pre¬ 
sented only for cases where it may be economically advantageous to make such a change. How¬ 
ever, there may be other restrictions (i.e., operating labor, space) to making the operational changes 
in question. In other cases, there may be more than one equally viable technology. At that point, 
the water utility should further evaluate its preferences with respect to costs and labor commit¬ 
ments, and capabilities with respect to residuals disposal and facility expansion. 

The decision trees employ the following labeling scheme: 


The Question/Decision block requests information or utility preference in the form of a yes/no or 
multiple-choice question. The Action Box provides the recommended follow-up action given sys¬ 
tem-specific constraints and preferences. This box is frequently used as the stopping point for a 
particular branch of the decision tree. The Reference Box simply directs the utility to another 
portion of the decision tree. 

If a utility reaches an action box pertaining to switching sources, blending, or existing treatment 
optimization, they should refer to Section 2 for more specific information. If a utility reaches an 
action box pertaining to new treatment installation, they should refer to Section 4 for cost informa¬ 
tion and Sections 6-8 for specific design considerations. 

The decision trees are intended for use as an iterative tool. If a utility proceeds to a specific action 
box, conducts follow-up cost estimation, process optimization, and/or pilot-testing, and the results 
indicate that the selected strategy may be ineffective or too expensive for arsenic removal, the 
utility can restart the tree and modify preferences. 

The following assumptions were made in the development of the decision trees: 

• Optimization of existing treatment process is economically preferable over new installations. 

• Construction of new conventional gravity coagulation/filtration or LS systems is not appropri¬ 
ate for the sole purpose of arsenic removal. 

• Small water systems would opt for disposable adsorptive media rather than conduct on-site 
regeneration. 

• Small systems would choose to not generate hazardous waste for either on-site treatment or off¬ 
site disposal. 


Question/Decision Box 


Action Box 




Reference Box 


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Decision Tree Overview 


Non -Treatment Alternatives 


□ Tree 1 Non-Treatment Alternatives 


Treatment Selection 


□ Tree 2 Treatment Selection 

• Tree 2a Enhanced Coagulation/Filtration 

• Tree 2b Enhanced Lime Softening 

• Tree 2c Iron & Manganese Filtration 


Selecting New Treatment 


□ Tree 3 Selecting New Treatment 

• Tree 3a Ion Exchange Processes 

• Tree 3b Sorption Processes 

• Tree 3c Filtration & Membrane Processes 


Figure 3-1. Decision Tree Overview. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


43 










Tree 1 

Non-Treatment Alternatives 


Does the Running Annual 
Average Arsenic Concentration 
exceed the MCL? 


Are there one or more 
other sources available 

N 

with arsenic levels below 
the MCL? 


1 

rV 


Can these sources be 
operated in lieu of the 

Y 

problematic source to meet 
total system demand? 



1 N 



Consider switching 
problematic source 
to back-up/seasonal 
use. Refer to 
Section 2.1.2 


Can these sources always 

N 

Would you prefer to 

be operated in conjunction 

site/install a new source 

with the high arsenic 

W 

before employing or 

sources? 


modifying treatment? 


I 


Can the sources be blended 
in a manner such that the 
arsenic MCL is met at all 
entry points to the system? 


Are there any constraints to 
blending, such as distance 
between sources, water 
quality impacts, water 
rights, etc.? 


N 


N 


Consider locating 
or installing a new 
source. Refer to 
Section 2.1.1 


Go to Tree 2 - “Treatment 
Selection” 



N 


Consider using 
blending to meet 
MCL. Refer to 
Section 2.1.3 


Figure 3-2. Decision Tree 1 - Non-Treatment Alternatives. 


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Tree 2 

Treatment Selection 



▼ ▼ 


Are the problematic source(s) 
treated beyond disinfection or 
corrosion control? 



N 


Have previous attempts to 
optimize existing treatment for 

y 

arsenic removal been made and 


failed? 


In 



Go to Tree 3 - 
“Selecting New Treatment” 


Identify Existing 
Treatment: 

— 

. .. .. 



Linic Softening 





Go to Tree 2a - 

“Enhanced Coagulation/Filtration’ 

Go to Tree 2b - 
“Enhanced Lime Softening” 


Go to Tree 2c - 

‘Iron & Manganese Filtration” 


*Pre-oxidized refers to the process 
of converting As(III) to As(V) 


Figure 3-3. Decision Tree 2 - Treatment Selection. 

Use this decision tree only after using Tree 1 “Non-Treatment Alternatives” 


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Tree 2a 

Enhanced Coagulation/Filtration 


Identify coagulant: 


Iron-based 


Aluminum-based 


Is the current process 
operated at pH < 8.5? 


Evaluate increasing 
Fe coagulant dose. 
Refer to Section 2.5.2 


Polymer 



Are you willing to 
install pH adjustment 
capabilities? 


N 


Evaluate adjusting pH to 5.5-8.5 
and increasing Fe coagulant dose. 
Refer to Section 2.5.2 


Is the current 
process operated 
at pH < 7.0? 

Y 


— 


Ln .... 



Evaluate increasing 
A1 coagulant dose. 
Refer to Section 2.5.2 


Are you willing 
to install pH 
adjustment capabilities? 

Y 


1 N ,. 


Y Y 


Are you willing to 
switch to or incorporate 
an iron-based coagulant? 

Y 



Evaluate adjusting pH to 5-7 and 
increasing A1 coagulant dose. 
Refer to Section 2.5.2 


N 


Evaluate switching to or 
incorporating an 
iron-based coagulant. 
Refer to Section 2.5.2 


Denotes alternate techniques 
that should be investigated. 


Add new treatment technology by 
going to Tree 3 - 
“Selecting New Treatment” 


L _ 


Figure 3-4. Decision Tree 2a - Enhanced Coagulation/Filtration. 
Use this decision tree only after using Tree 2 “Treatment Selection 


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Tree 2b 

Enhanced Lime Softening 



N 


-► 


Add new treatment 
technology by going to 
Tree 3- “Selecting New 
Treatment” 



Y 


Evaluate addition of 
iron (up to 5 mg/L). 
Refer to Section 2.5.1 


Figure 3-5. Decision Tree 2b - Enhanced Lime Softening. 

Use this decision tree only after using Tree 2 “Treatment Selection .” 


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Tree 2c 

Iron & Manganese Filtration 


Are filters capable of 

N 


handling an increase in iron 

-► 

Is pH <7.5? 

load? 





A 


Y 


N 


Y 



N 


▼ 

Are you 
willing to 
adjust the pH 
to < 7.5? 


Y 


_ ▼ 

Evaluate adjusting 
pH to < 7.5 
Refer to Section 2.5.5 


N 


Add new treatment 
technology by going 
to Tree 3 - 
“Selecting New 
Treatment” 


Figure 3-6. Decision Tree 2c - Iron/Manganese Filtration. 

Use this decision tree only after using Tree 2 “Treatment Selection .” 


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Tree 3 

Selecting New Treatment 


Are all of the following water 
quality criteria met at the 
problematic source? 

• S0 4 2 ' <50 mg/L 

• NO 3 - (as N) < 5 mg/L 

• TDS < 500 mg/L 

• pH >6.5 and < 9 


Go to Tree 3a - 
‘Ion Exchange Processes” 


J 

l N 

Is the source water: 

Y 

Fe < 0.5 mg/L, and 

-— 1 

Mn < 0.05 mg/L. 



N 


Go to Tree 3b - 
“Sorption Processes” 


Go to Tree 3c - 

“Filtration & Membrane Processes” 


Figure 3-7. Decision Tree 3 - Selecting New Treatment. 

Use this decision tree only after using Tree 2 “Treatment Selection .” 


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Tree 3a 

Ion Exchange Processes 



* This evaluation will be complex because removal of As from drinking water will change the 
background As concentration for the TBLL. A revised TBLL would be used to determine if the 
brine stream could be discharged to the POTW. TDS may be the more critical restriction, 
especially in the western U.S. 


Figure 3-8. Decision Tree 3a - Ion Exchange Processes. 

Use this decision tree only after using Tree 3 “Selecting New Treatment .” 


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Tree 3b 

Sorption Processes 



Figure 3-9. Decision Tree 3b - Sorption Processes. 

Use this decision tree only after using Tree 3 “Selecting New Treatment .” 


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Tree 3c 

Filtration & Membrane Processes 



Is the source water 
Fe:As Ratio > 
20:1? 

Y , 



N 



Evaluate Pre-Engineered 
Microfiltration ( refer to 
Section 2.5.3) or Pre- 
Engineered Direct Filtration 
(refer to Sections 2.5.4 & 7). 


Evaluate Iron Coagulant 
Addition with Pre- 
Engineered Microfiltration 
(refer to Section 2.5.3 ) or 
Pre-Engineered Direct 
Filtration (refer to Sections 
2.5.4 & 7). 


Figure 3-10. Decision Tree 3c - Filtration and Membrane Processes. 
Use this decision tree only after using Tree 3 “Selecting New Treatment .” 


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Table 3-3 provides a summary of information about the different alternatives for arsenic mitigation 
found in this Handbook. 


Table 3-3. Arsenic Treatment Technologies Summary Comparison. 

(1 of 2) 


Factors 

Sorphon Processes 

Membrane 

Processes 

Ion Exchange 

Activated Alumina A 

Iron Based 

Sorbents 

Reverse 

Osmosis 

IX 

AA 

IBS 

RO 

USEPA BAT B 

Yes 

Yes 

No c 

Yes 

USEPA SSCT B 

Yes 

Yes 

No c 

Yes 

System Size BD 

25-10,000 

25-10,000 

25-10,000 

501-10,000 

SSCT for POU 8 

No 

Yes 

No c 

Yes 

POU System Size BD 

- 

25-10,000 

25-10,000 

25 -10,000 

Removal Efficiency 

95% E 

95% E 

up to 98% E 

> 95% E 

Total Water Loss 

1-2% 

1-2% 

1- 2% 

15-75% 

Pre-Oxidation Required F 

Yes 

Yes 

Yes 0 

Likely H 

Optimal Water 

Quality Conditions 

pH 6.5 - 9 E 

< 5 mg/L N0 3 ' 1 

< 50 mgA S0 4 2 ' j 

< 500 mgT. TDS K 

< 0.3 NTU Turbidity 

pH 5.5-6 1 
pH 6 - 8.3 L 
< 250 mg/L Cl 1 
< 2 mg/L F" 1 

< 360 mg/L S0 4 2 ’ K 

< 30 mg/L Silica M 

< 0.5 mg/L Fe~ 3 1 

< 0.05 mg/L Mn* 2 1 

< 1,000 mg/L TDS K 

< 4 mg/L TOC K 

< 0.3 NTU Turbidity 

pH 6 - 8.5 
< 1 mg/L PO; 3N 
< 0.3 NTU Turbidity 

No Particulates 

Operator Skill Required 

High 

Low A 

Low 

Medium 

Waste Generated 

Spent Resin, Spent Brine, 
Backwash Water 

Spent Media, Backwash 
Water 

Spent Media, Backwash 
Water 

Reject Water 

Other Considerations 

Possible pre & post pH 
adjustment. 

Pre-filtration required. 
Potentially hazardous brine 
waste. 

Nitrate peaking. 
Carbonate peaking affects pH. 

Possible pre & post pH 
adjustment. 

Pre-filtration may be 
required. 

Modified AA available. 

Media may be very 
expensive. 0 

Pre-filtration may be 
required. 

High water loss (15- 
75% of feed water) 

Centralized Cost 

Medium 

Medium 

Medium 

High 

POU Cost 

- 

Medium 

Medium 

Medium 


A Activated alumina is assumed to operate in a non-regenerated mode. 

B USEPA, 2002a. 

c IBS's track record in the US was not established enough to be considered as Best Available Technology (BAT) or Small System Compliance 
Technology (SSCT) at the time the rule was promulgated. 

D Affordable for systems with the given number of people served. 

E USEPA, 2000. 

F Pre-oxidation only required for As(III). 

G Some iron based sorbents may catalyze the As(lII) to As(V) oxidation and therefore would not require a pre-oxidation step. 

H RO will remove As(III), but its efficiency is not consistent and pre-oxidation will increase removal efficiency. 

1 AwwaRF, 2002. 

J Kempic, 2002. 

K Wang, 2000. 

L AA can be used economically at higher pHs, but with a significant decrease in the capacity of the media. 

M Clifford, 2001. 

N Tumalo, 2002. 

0 With increased domestic use, IBS cost will significantly decrease. 


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Table 3-3. Arsenic Treatment Technologies Summary Comparison. 

(2 of 2) 



Precipitative Processes 

Factors 

Enhanced Lime 
Softening 

Enhanced 

(Conventional) 

Coagulation 

Filtration 

Coagulation- 

Assisted 

Micro- 

Filtration 

Coagulation- 
Assisted Direct 
Filtration 

Oxidation 

Filtration 


LS 

CF 

CMF 

CADF 

OxFilt 

USEPA BAT B 

Yes 

Yes 

No 

Yes 

Yes 

USEPA SSCT B 

No 

No 

Yes 

Yes 

Yes 

System Size BX> 

25-10,000 

25-10,000 

500-10,000 

500-10,000 

25-10,000 

SSCT for POU B 

No 

No 

No 

No 

No 

POU System Size BD 

- 

- 

- 

- 

- 

Removal Efficiency 

90% E 

95% (w/ FeCl,) E 
< 90% (w/ Alum) E 

90% E 

90% E 

50-90% E 

Total Water Loss 

0% 

0% 

5% 

1-2% 

1-2% 

Pre-Oxidation Required F 

Yes 

Yes 

Yes 

Yes 

Yes 

Optimal Water 

Quality Conditions 

pH 10.5 - 11 1 
> 5 mg/L Fe +31 

pH 5.5 - 8.5 p 

pH 5.5 - 8.5 p 

pH 5.5 - 8.5 p 

pH 5.5 - 8.5 
>0.3 mgA Fe 
FeAs Ratio > 20:1 

Operator Skill Required 

High 

High 

High 

High 

Medium 

Waste Generated 

Backwash Water, 
Sludge (high volume) 

Backwash Water, 
Sludge 

Backwash Water, 
Sludge 

Backwash Water, 
Sludge 

Backwash Water, 
Sludge 

Other Considerations 

Treated water requires pH 
adjustment. 

Possible pre & post 
pH adjustment. 

Possible pre & 
post pH 
adjustment. 

Possible pre & post 
pH adjustment. 

None. 

Centralized Cost 

Low 0 

Low Q 

High 

Medium 

Medium 

POU Cost 

N/A 

N/A 

N/A 

N/A 

N/A 


B USEPA, 2002a. 

D Affordable for systems with the given number of people served. 

E Depends on arsenic and iron concentrations. 

F Pre-oxidation only required for As(III). 

1 AwwaRF, 2002. 
p Fields, et aL, 2002a. 

Q Costs for enhanced LS and enhanced CF are based on modification of an exisitng technology. Most small systems will not have this technology in 
place. 


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Section 4 

Planning-Level Treatment Costs 


This section presents information the utility can use to calculate planning-level capital and O&M 
costs for the treatment method selected in Section 3. All the charts are from Technologies and 
Costs for Removal ofArsenic from Drinking Water (USEPA, 2000). This information will give the 
utility only a rough estimate of the selected treatment process costs so that relative costs can be 
evaluated. If the costs are too high, the utility is encouraged to re-evaluate the criteria used in the 
treatment selection process in Section 3. 

It is critical that the utility employ the decision trees in Section 3, rather than the cost corre¬ 
lation curves provided in this section, as the primary tool for selecting an arsenic mitigation 
strategy. The trees take into account system-specific conditions and utility preferences. Compar¬ 
ing planning-level costs without consideration of the technical issues incorporated in the decision 
trees may lead the utility to an inappropriate technology. 

The cost curves incorporate different mathematical models for different sized systems. Because of 
this, there are step changes between the model outputs in some of the charts. If the system being 
sized falls at a flowrate that lays on one of these step changes, the utility is encouraged to use an 
average cost number and then perform a more site specific cost evaluation. 

Capital cost charts are based on the maximum flowrate for which the facility was designed (i.e., 
design flowrate). The design flowrate should be higher than the treated flowrate determined in 
Section 3. The capital costs include: process costs (including manufactured equipment, concrete, 
steel, electrical and instrumentation, and pipe and valves), construction costs (including site-work 
and excavation, subsurface considerations, standby power, contingencies, and interest during con¬ 
struction), engineering costs (including general contractor overhead and profit, engineering fees, 
and legal, fiscal, and administrative fees) and the costs associated with retrofitting, permitting, pilot 
testing, housing, and system redundancy (where prudent). The capital costs do not include costs 
associated with additional contaminants or land. 

The O&M costs are based on the average flowrate that the facility is expected to treat. The O&M 
costs are based on the following assumptions: 

• Electricity costs of $0.08/kWh, 

• Diesel fuel costs of $ 1.25/gallon, 

• Natural gas costs of $0.006/scf, 

• Large systems labor costs of $40/h (or loaded labor costs of $52/h), 

• Loaded labor costs for small systems of $28/h, and 

• Building energy use of 102.6 kWh/sft/y. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


55 








All of the costs presented in the charts are given in year 1998 dollars. To escalate the capital cost of 
a technology from 1998 to the present, construction cost indexes (CCI) published by Engineering 
News Record (ENR) can be used in the following formula. 


Where: 

■^Current 

P 

C^Current 

CCI1998 


^Current ^1998 


f 

v. 


rrT 

Current 

CCI1998 


) 


= Present Cost, 

= Year 1998 Cost (from the charts), 

= Construction Cost Index Value for the current year, and 
= Construction Cost Index Value for 1998. 


Eqn. 4-1 


For example, a greensand filtration system is designed to handle 1 MGD. Values taken from the 
figures and their equations are: 

• 1998 Capital Cost is $587,584 (Figure 4-21) 

• 1998 Waste Disposal Capital Cost is $3,955 (Figure 4-23) 


The annual average 20-cities ENR CCI for 1998 and for November 2002 are 5,920.44 and 6,578.03, 
respectively. Therefore, the total capital cost for this facility can be estimated for the year 2002 
using Equation 4-1 as follows: 


^Capital, 2002 


($587,584 + 53,955) 


^6,578.03 
v 5,920.44 


) 


$657,242 


The O&M costs presented in the Handbook are 1998 costs and can be escalated to the current year’s 
costs using the formula below. This formula can also be used in place of the CCI equation, al¬ 
though it is less accurate. 


Pcurrent =Pl998(l + i) (Ycurrem 

Where: 

P„ f = Current Cost, 

Current 

P 19 q 8 = Year 1998 Cost (from the charts), 

i = Annual rate of inflation (currently ~ 2.5% - 3%), and 
Y„ , = Current Year. 

Current 


Eqn. 4-2 


Using the same example of a 1 MGD greensand filtration system, the values taken from the figures 
and their equations are: 

• 1998 O&M cost is $66,314/y (Figure 4-22) 

• 1998 Waste Disposal O&M cost is $8,678/y (Figure 4-24) 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


56 









Capital Cost ($) 


Assuming an annual inflation rate of 2.5%, the O&M can be estimated for the year 2002 using 
Equation 4-2 as follows: 


P 0&M, 2002 = ($66,314 + $8,678) (l + 0.025) (2002_1998) = $82,777 

Additionally, the USEPA has a cost model for estimating the costs of processes using sorptive 
media. This cost model, titled Cost Estimating Program for Arsenic Removal by Small Drinking 
Water Facilities , can be found on the USEPA’s website. 

4.1 Pre-Oxidation System Costs Using Chlorine 

Costs presented in the following charts make the following assumptions: 

• A new chlorination system is installed. 

• A dose of 1.5 mg/L of free chlorine is added to the treated flow. 

• Systems use 15% sodium hypochlorite feed stock and are designed to handle dosages as high as 
10 mg/L. 


$ 100,000 


$10,000 


$ 1,000 


0.01 


0.1 1 

Design Flowrate (mgd) 


w/o Housing-w/ Housing 



10 


Figure 4-1. Chlorination Capital Costs. 


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O&M Cost ($/y) 


$ 100,000 


$ 10,000 


$ 1,000 


0.001 


0.01 


0.1 














-4- 

-4 




— — L 

— I 

— J 

— 

1 


















— L 




L 























y - -u.jyzoxi- ozj.^x ■+- iy,jou 






















\ 























* 
















































































































\ 

\ 









y 

= _ 

1E-10x 2 +4,239.7x+ 1,161.8 



y = 4,920.lx + 916.9 








\ 

4 










TT 

-TT 







_ 









Average Flowrate (mgd) 
Figure 4-2. Chlorination O&M Costs. 

4.2 Ion Exchange System Costs 


10 


Costs presented in the following charts make the following assumptions: 

• A new IX system is installed. 

• Capital Cost Design Assumptions: 

O Pre-oxidation is required but not included in these costs. 

O Cost includes a redundant column to allow the system to operate during regeneration. 

• O&M Cost Design Assumptions: 

O Run length when sulfate is at or below 20 mg/L is 1500 bed volumes (BV). 

O Run length when the sulfate is between 20 and 50 mg/L is 700 BV. 

O Labor rate for small systems is $28/hour. The loaded labor rate for large systems is $52/ 
hour. 

• Waste is discharged to a POTW (i.e., indirect discharge). 


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O&M Cost ($/y) Capita] Cost ($) 



0.01 0.1 1 10 


Design Flowrate (mgd) 


Figure 4-3. Ion Exchange (<20 mg/L S0 4 2 ') Capital Costs. 


0.001 


0.01 



0.1 

Average Flowrate (mgd) 


10 


Figure 4-4. Ion Exchange (<20 mg/L S0 4 2 ) O&M Costs. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


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O&M Cost ($/y) 


0.01 


0.1 


1 


10 


Design Flowrate (mgd) 

Figure 4-5. Ion Exchange (<20 mg/L S0 4 2 ') Waste Disposal Capital Costs. 



0.001 0.01 0.1 1 10 

Average Flowrate (mgd) 

Figure 4-6. Ion Exchange (<20 mg/L S0 4 2 ) Waste Disposal O&M Costs. 


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O&M Cost ($/y) Capital Cost ($) 



Design Flowrate (mgd) 


Figure 4-7. Ion Exchange (20-50 mg/L S0 4 2 ) Capital Costs. 


0.001 


0.01 


0.1 

Average Flowrate (mgd) 



10 


Figure 4-8. Ion Exchange (20-50 mg/L S0 4 2 ) O&M Costs. 


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$10,000 


*-» 

(Z> 

O 

u 

'a 

U 


$ 1,000 

0.01 0.1 1 10 

Design Flowrate (mgd) 

Figure 4-9. Ion Exchange (20-50 mg/L S0 4 2 ) Waste Disposal Capital Costs. 



















































































































y — j,uoj 

Ml ■ ■- 














V 








y = 

3 

,955 ^^ 









y 

= 21 

47 


5 

,1 ( 

?8 











































































0.001 0.01 0.1 1 10 

Average Flowrate (mgd) 

Figure 4-10. Ion Exchange (20-50 mg/L S0 4 2 ) Waste Disposal O&M Costs. 


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Capital Cost ($) 


4.3 Activated Alumina System Costs 


Costs presented in the following charts make the following assumptions: 

• A new AA system is installed. 

• AA media is disposed of in a non-hazardous landfill rather than regenerated. 

• Four treatment modes are assumed: 

O No pH adjustment, Natural pH of 7-8, run length is 10,000 BV. 

O No pH adjustment, Natural pH of 8-8.3, run length is 5,200 BV. 

O pH adjusted to 6.0 using hydrochloric acid, run length is 23,100 BV. 

O pH adjusted to 6.0 using sulfuric acid, columns are good for 15,400 BV. 

• Capital Cost Design Assumptions: 

O Redundant column included for operation during media replacement. 

O Costs for constructing housing for the equipment are included. 

O Capital costs include both pre- and post-treatment pH adjustment if pH adjustment is used. 

• O&M Cost Design Assumptions: 

O Power costs are $0.08/kwh. 

O pH adjustment costs are included. 

O Labor rate for small systems is $28/hour. The loaded labor rate for large systems is $52/ 
hour. 



0.01 0.1 1 10 

Design Flowrate (mgd) 

Figure 4-11. Activated Alumina (Natural pH) Capital Costs. 


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0.001 0.01 0.1 1 10 

Average Flowrate (mgd) 

Figure 4-12. Activated Alumina (Natural pH of 7-8) O&M Costs. 



0.001 0.01 0.1 1 10 

Average Flowrate (mgd) 


Figure 4-13. Activated Alumina (Natural pH of 7-8) Waste Disposal O&M Costs. 


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O&M Cost ($/y) O&M Cost ($/y) 



0.001 0.01 0.1 1 10 

Average Flowrate (mgd) 

Figure 4-14. Activated Alumina (Natural pH of 8-8.3) O&M Costs. 


51,000,000 


$ 100,000 


$ 10,000 


$ 1,000 


$100 


$10 



0.001 


0.01 


0.1 

Average Flowrate (mgd) 


10 


Figure 4-15. Activated Alumina (Natural pH of 8.0-8.3) Waste Disposal O&M Costs. 


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0.01 0.1 1 10 

Design Flowrate (mgd) 


Figure 4-16. Activated Alumina (pH Adjusted to 6.0) Capital Costs. 


$10,000,000 


$1,000,000 




C/5 

© 

u 


° $ 100,000 


3 

o 


$ 10,000 


$ 1,000 


0.001 


0.01 


0.1 



1 


10 


Average Flowrate (mgd) 

Figure 4-17. Activated Alumina (pH adjusted to 6.0 - 23,100 BV) O&M Costs. 


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0.001 0.01 0.1 1 10 

Average Flowrate (mgd) 

Figure 4-18. Activated Alumina (pH adjusted to 6.0 - 23,100 BY) Waste Disposal O&M Costs. 


$10,000,000 


$1,000,000 




$ 100,000 


3 

o 


$ 10,000 



Average Flowrate (mgd) 

Figure 4-19. Activated Alumina (pH adjusted to 6.0 - 15,400 BY) O&M Costs. 


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O&M Cost ($/y) 



0.001 0.01 0.1 1 10 

Average Flowrate (mgd) 

Figure 4-20. Activated Alumina (pH adjusted to 6.0 - 15,400 BV) Waste Disposal O&M Costs. 


4.4 Iron Based Sorbent System Costs 

IBS are relatively new technologies and, as such, costs for IBS treatment systems have not yet been 
developed. 

4.5 Greensand System Costs 

Costs presented in the following charts make the following assumptions: 

• A new greensand filtration system is installed. 

• Potassium permanganate feed rate of 10 mg/L (however, chlorination will work also). 

• Hydraulic loading rate of 4 gpm/sft. 

• Backwash flowrate of 10-12 gpm/sft. 

• Backwash waste is discharged to a POTW (i.e., indirect discharge). 


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O&M Cost ($/y) Capital Cost ($) 



0.01 0.1 1 10 

Design Flowrate (mgd) 


Figure 4-21. Greensand Capital Costs. 


0.001 


0.01 


0.1 

Average Flowrate (mgd) 



10 


Figure 4-22. Greensand O&M Costs. 


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O&M Cost ($/y) Capital Cost ($) 


$ 10,000 


$ 1,000 -- 

0.01 0.1 1 



Design Flowrate (mgd) 


Figure 4-23. Greensand Waste Disposal Capital Costs. 



0.001 0.01 0.1 1 

Average Flowrate (mgd) 

Figure 4-24. Greensand Waste Disposal O&M Costs. 


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Capital Cost ($) 


4.6 Coagulation Assisted Microfiltration System Costs 


Costs presented in the following charts make the following assumptions: 

• Ferric chloride dose of 25 mg/L. 

• For Systems Less Than 1 MGD: 

O Package plants with a hydraulic loading rate of 5 gpm/sft. 

O Sodium hydroxide dose of 20 mg/L for pH control. 

O Standard MF. 

• For Systems Larger Than 1 MGD: 

O Rapid mix for 1 minute. 

O Flocculation for 20 minutes. 

O Sedimentation at 1000 gpd/sft using rectangular tanks. 

O Standard MF. 

• Waste is dewatered before being disposed of in a non-hazardous landfill. Costs are given for 
dewatering performed either mechanically or non-mechanically. Land costs are not included in 
the waste disposal costs. 



Figure 4-25. Coagulation Assisted Microfiltration Capital Costs. 


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$1,000,000 




Q $ 100,000 


o 


$ 10,000 


0.001 


0.01 


0.1 1 
Average Flowrate (mgd) 



10 


Figure 4-26. Coagulation Assisted Microfiltration O&M Costs. 



0.01 0.1 1 10 

Design Flowrate (mgd) 


Figure 4-27. Coagulation Assisted Microfiltration (w/ Mechanical Dewatering) Waste Disposal 

Capital Costs. 


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0.001 0.01 0.1 1 10 

Average Flowrate (mgd) 


Figure 4-28. Coagulation Assisted Microfiltration (w/ Mechanical Dewatering) Waste Disposal 

O&M Costs. 



0.01 0.1 1 10 

Design Flowrate (mgd) 


Figure 4-29. Coagulation Assisted Microfiltration (w/ NonMechanical Dewatering) Waste 

Disposal Capital Costs. 


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O&M Cost ($/y) 


0.001 


0.01 


0.1 

Average Flowrate (mgd) 



10 


Figure 4-30. Coagulation Assisted Microfiltration (w/ NonMechanical Dewatering) Waste 

Disposal O&M Costs. 

4.7 Coagulation/Filtration System Enhancement Costs 

Costs presented in the following charts make the following assumptions: 

• A coagulation/filtration system is already installed. Costs are only for system enhancement for 
arsenic removal. 

• Assumptions about the Existing Coagulation/Filtration System: 

O Existing coagulation/filtration system removes 50% of the arsenic without enhancement. 
O Ferric chloride dose of 25 mg/L. 

Q Polymer dose of 2 mg/L. 

O Lime dose of 25 mg/L for pH control. 

O Systems less than 1 MGD are package plants with a hydraulic loading rate of 5 gpm/sft. 

O Systems Larger Than 1 MGD: 

■ Rapid mix for 1 minute. 

■ Flocculation for 20 minutes. 

■ Sedimentation at 1000 gpd/sft using rectangular tanks. 

■ Dual media gravity filters running at a hydraulic loading rate of 5 gpm/sft. 

• Assumptions for the Enhancement of the Coagulation/Filtration System: 

O Additional ferric chloride dose of 10 mg/L. 

O Additional feed system for increased ferric chloride dose. 

O Additional lime dose of 10 mg/L for pH adjustment. 

O Additional feed system for increased lime dose. 


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O&M Cost ($/y) Capital Cost ($) 


$1,000,000 


$ 100,000 


$ 10,000 


$ 1,000 


0.01 


0.1 1 
Design Flowrate (mgd) 



10 


Figure 4-31. Coagulation/Filtration System Enhancement Capital Costs. 



0.01 0.1 1 10 

Average Flowrate (mgd) 


Figure 4-32. Coagulation/Filtration System Enhancement O&M Costs.Lime Softening System 

Enhancement Costs 


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Capital Cost ($) 


4.8 Lime Softening System Enhancement Costs 


Costs presented in the following charts make the following assumptions: 

• An LS system is already installed. Costs are only for system enhancement for arsenic removal. 

• Lime dosage of 250 mg/L. 

• Carbon dioxide dosage of 35 mg/L for recarbonation. 

• Assumptions about the Existing LS System: 

O Systems less than 1 MGD are package plants. 

O Systems Larger Than 1 MGD: 

■ Rapid mix for 1 minute. 

■ Flocculation for 20 minutes. 

■ Sedimentation at 1500 gpd/sft using circular tanks. 

■ Dual media gravity filters running at a hydraulic loading rate of 5 gpm/sft. 

• Assumptions for the Enhancement of Existing LS System: 

O Additional lime dose of 50 mg/L. 

O Additional feed system for increased LS dose. 

O Additional carbon dioxide dose of 35 mg/L for recarbonation. 

O Additional feed system for increased carbon dioxide dose. 

$10,000,000 


$1,000,000 


$100,000 


$ 10,000 


$ 1,000 

0.01 0.1 1 10 

Design Flowrate (mgd) 



Figure 4-33. Lime Softening Enhancement Capital Costs. 


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O&M Cost ($/y) 


$1,000,000 


$ 100,000 


$ 10,000 


$ 1,000 



Average Flowrate (mgd) 


Figure 4-34. Lime Softening Enhancement O&M Costs. 

4.9 Point-of-Use Reverse Osmosis System Costs 

Costs presented in the following charts make the following assumptions: 

• In an average household, there are 3 individuals using 0.53 gallon each per day for a total of 579 
gallons per year. 10 

• Life of POU unit is 5 years. 

• Duration of cost study is 10 years. 

• Cost of water meter and automatic shut-off valve included. 

• No shipping and handling included. 

• If the water is chlorinated, dechlorination may be required. Costs for dechlorination are not 
included. 

• Volume discount schedule—retail for a single unit, 10 percent discount for 10 or more units, 15 
percent discount on more than 100 units. 

• Installation time—1 hour unskilled labor (POU) 

• Minimally skilled labor—$14.50 per hour (population less than 3,300 individuals). 

• Skilled labor—$28 per hour (population greater than 3,300 individuals). 

• O&M costs include maintenance, replacement of pre-filters and membrane cartridges, labora¬ 
tory sampling and analysis, and administrative costs. 


10 USEPA, 1998. 


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O&M Cost ($) Capital Cost ($) 



10 


100 


1000 


Households 


10000 


Figure 4-35. POU Reverse Osmosis Capital Costs. 



Households 


Figure 4-36. POU Reverse Osmosis O&M Costs. 


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Capital Cost ($) 


4.10 Point-of-Use Activated Alumina System Costs 


Costs presented in the following charts make the following assumptions: 

• In an average household, there are 3 individuals using 0.53 gallon each per day for a total of 579 
gallons per year. 11 

• Life of POU unit is 5 years. 

• Duration of cost study is 10 years. 

• Cost of water meter and automatic shut-off valve included. 

• No shipping and handling included. 

• Volume discount schedule—retail for a single unit, 10 percent discount for 10 or more units, 15 
percent discount on more than 100 units. 

• Installation time—1 hour unskilled labor (POU) 

• Minimally skilled labor—$14.50 per hour (population less than 3,300 individuals). 

• Skilled labor—$28 per hour (population greater than 3,300 individuals). 

• O&M costs include maintenance, replacement of pre-filters and membrane cartridges, labora¬ 
tory sampling and analysis, and administrative costs. 



Figure 4-37. POU Activated Alumina Capital Costs. 


11 USEPA, 1998. 


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O&M Cost ($) 



Figure 4-38. POU Activated Alumina O&M Costs. 


4.11 Point-of-Use Iron Based Sorbent System Costs 

Iron based sorbents (IBS) are relatively new technologies and, as such, the costs for using small IBS 
units in a POU scheme have not been well defined. Costs for an IBS POU system are anticipated to 
be similar to those of an AA POU system. 


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Section 5 

Pre-Oxidation Design Considerations 


The conversion of reduced inorganic As(III) to As(V) is critical for achieving optimal performance 
of all unit processes described in this Handbook. Conversion to As(V) can be accomplished by 
providing an oxidizing agent at the head of any proposed arsenic removal process. Chlorine and 
permanganate are highly effective for this purpose. They oxidize As(III) to As(V) within one 
minute in the pH range of 6.3 to 8.3. Ozone rapidly oxidizes As(III) but its effectiveness is signifi¬ 
cantly diminished by the presence of sulfides or TOC. Solid phase oxidants such as Filox-R™ have 
also been shown to oxidize As(III). Chlorine dioxide and monochloramine are ineffective in oxi¬ 
dizing As(III). UV light, by itself is also ineffective. However, if the water is spiked with sulfite, 
UV photo-oxidation shows promise. Because of these considerations, only chlorine, permangan¬ 
ate, ozone, and solid phase oxidants are discussed in this section. 

5.1 Chlorine Pre-Oxidation Design Considerations 

The primary applications of chlorine in water treatment include pre-oxidation, primary disinfec¬ 
tion, and secondary disinfection. Several arsenic removal processes, particularly membranes, are 
chlorine sensitive and/or intolerant. In these instances, the utility should consider an alternate 
oxidation technology. If this is the case, but the system already has chlorination capabilities in 
place, the process of modifying the existing system to achieve As(III) oxidation is complicated. 
One alternative is the application of a pre-chlorination—dechlorination—arsenic removal—re-chlo- 
rination treatment setup. However, this alternative may be more costly than integrating a perman¬ 
ganate pre-oxidation system. 

Chlorine can be added either as liquid sodium hypochlorite (Equation 5-1) or dissolved gas (Equa¬ 
tion 5-2). In either case, biocidal hypochlorous acid is generated. 

NaOCl + H 2 0 -> HOC1 + NaOH Eqn. 5-1 

Cl 2 + H 2 0 HOC1 + HC1 Eqn. 5-2 

The first step in selecting the most appropriate method of chlorination is to determine the chlorine 
flow requirements for the particular application. Chlorine demand can be calculated with Equation 
5-3. 


where: 


M 


Cl 2 


M c < =Q-5 


( 


ci. 


0.012 


min L lb 


V 


d gal mg 


= Chlorine Mass Flow (lb/day of Cl 2 ), 


Eqn. 5-3 


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Q = Design Flow Rate (gpm), and 
5 cl2 = Chlorine Dose (mg/L as Cl 2 ). 

Careful consideration should be given to the chlorine dose estimate. Most waters contain sub¬ 
stances other than As(III) that exert chlorine demand. In many cases, these substances compete for 
chlorine more aggressively than As(III). Section 2.2.1 lists the chlorine demand for the stoichio¬ 
metric conversion of As(III), Fe 2+ , Mn 2+ , and FIS'. Chlorine will also react with ammonia and TOC. 
Simple chlorine demand bench testing can be used to ascertain the instantaneous and ultimate 
chlorine demand of particular water. The applied chlorine dose should be three times the ultimate 
chlorine demand. 


5 ci 2 =3 d ci 2 Eqn. 5-4 

Where: 

5 c , 2 = Chlorine Dose (mg/L as Cl 2 ), and 

d ci 2 = Ultimate Chlorine Demand (mg/L as Cl 2 ). 

Selection of the type of chlorination system should include consideration of capital and operating 
costs, O&M requirements, code restrictions, containment requirements, footprint, and safety con¬ 
cerns. This Handbook will address the following options, which are considered most viable for 
small water systems: 

• Commercial liquid hypochlorite feed system 

• On-site hypochlorite generation system 

The application of chlorine gas for chlorination is not discussed as it is more hazardous, frequently 
more expensive, and frequently less applicable to small systems. 

5.1.1 Commercial Liquid Hypochlorite 

Liquid sodium hypochlorite can be purchased as a 5%% or 12!/2% strength solution. The 
solution must be delivered to the facility by tanker trucks or in drums on a regular basis. 
The solution is stored on-site in a tank and metered into the system by a small pump. Figure 
5-1 shows a flow diagram for a typical liquid hypochlorite process. Figure 5-2 is a typical 
flow schematic for a flooded suction hypochlorite metering system. 


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82 



12 - 15 % 
Hypochlorite 
Storage Tank 



Chlorinated 

Water 


Figure 5-1. Typical Liquid Hypochlorite Process Flow Diagram. 


MAIN 

CONNECTION 


PROCESS 

LINE 


"SI 


M- 


SUPPLYTANK 


BACKPRESSURE 


4 , 


fP 3 


— J/ 


VALVE 


VALVE 

PRESSURE RELIEF \I 
VALVE 


=> 


I p-i'-r 1—1 




SUCTION 
SHUT-OFF VALVE 


UNION \ 


PULSATION 

DAMPENER 

r VALVE 


4 


4 — 03—4 


J=> ^ 

VALVE —' 

4-1 


F 

TO DRAIN 
OR SUPPLY 


— IS" MIN — 

i - 1 


T 1 

f.." 1 ^ ^— 

KEEP TO MIN. 

UNION -A 1 

DISTANCE 

DISCHARGE J 

\ 

DRAIN VALVE 


UNION 


TO WASTE 
OR SUPPLY 

CALIBRATION 

CHAMBER 




V STRAINER 


1 -M - 


J 


-f 


<3 -4 - 4 - 


VALVE 



UNION 


SUCTION 
DRAIN PLUG 
OR VALVE 


Figure 5-2. Liquid Hypochlorite System Schematic (USFilter, Wallace & Tieman). 


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The flow rate of liquid hypochlorite required to meet chlorine mass flow requirements can 
be approximated by Equation 5-5. This flow rate should be used to size the metering pump, 
as well as provide an estimate of chemical operating costs. 



Eqn. 5-5 


2 C 24 hr 
v -xi 2 y z, ^ Ui J 


Where: 


Qd, = Hypochlorite Metering Pump Rate (gph) and 
Mq 2 = Chlorine Mass Flow (lb/day of Cl 2 ). 

C C i 2 = Concentration of Chlorine Solution (lbs Cl 2 /gal). 


For 12.5 wt% Sodium Hypochlorite, the concentration is 1.26 lbs/gal. 
For 5.25 wt% Sodium Hypochlorite, the concentration is 0.47 lbs/gal. 
For 0.008 wt% Sodium Hypochlorite, the concentration is 0.068 lbs/gal. 


The required capacity of the storage tank is contingent upon the desired frequency of tanker 
truck deliveries. Tanks are commonly sized to provide 7-21 days of storage. Because 
commercial strength liquid hypochlorite is a Class 1 Liquid Oxidizer, storage of more than 
4,000 pounds represents a non-exempt quantity and requires special precautions. The stor¬ 
age volume required may be calculated as follows. 



Eqn. 5-6 


Where: 


V = Storage Volume (gal), 

Qci, = Hypochlorite Metering Pump Rate (gph), and 
t = Storage Time (days). 


5.1.2 On-Site Hypochlorite Generation 

On-site generation of sodium hypochlorite is accomplished by adding electricity to a satu¬ 
rated (32%) brine solution. The strength of hypochlorite produced is 0.8%, which is below 
the hazardous material threshold of 1%. These systems can be constructed piecewise or 
purchased as pre-engineered units. 

Figure 5-3 shows a typical flow diagram for an on-site hypochlorite generation system. The 
equipment requirements of an on-site generation system, which can be seen in Figure 5-4, 
include a salt saturator, hypochlorite storage tanks, electrolyzers, rectifiers, controls, and 
hypochlorite metering pumps. The following material inputs are required per pound of 
chlorine generated: 3.5 lbs NaCl salt, 15 gallons of water, and 2.5 kWh of electrical energy. 

Figure 5-5 shows an on-site hypochlorite generator that will produce up to 36 lbs of chlorine 
per day. 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 84 









Raw 

Water 



Figure 5-3. Typical On-Site Hypochlorite Generation Process Flow Diagram. 



Sodium 
Hypochlorite 
Solution 


Hydrogen Discharge 
Power Supply/Rectifier 


Interstage 
Hydrogen Gas 
Take-off \ 


Electrolyzer 


Bellows Pump 


Salt Saturator 


Sodium Hypochlorite 
^/Storage Tank 

Sodium Hypochlorite 
Metering Pump 


Control Panel 
with HMI 


Dilution 

Water 


Blowers 

Primary and Back-up 


Water Main 


Water Supply 


Water Softener 


Brine Solution 


Figure 5-4. On-Site Hypochlorite Generation System Schematic (USFilter, Wallace & Tieman). 


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Figure 5-5. On-Site Hypochlorite Generation System (Severn Trent Services). 

5.2 Permanganate Pre-Oxidation Design Considerations 

The primary applications of permanganate (Mn0 4 ) in water treatment include preoxidation (par¬ 
ticularly for iron and manganese) and taste and odor control. Potassium permanganate exists in 
solid, granular form, but is typically applied as a saturated liquid (60 g/L at room temperature). 

Permanganate is not biocidal against drinking water pathogens, so there should be negligible re¬ 
sidual leaving the treatment works. Manganese particulates (MnCf) are produced as a result of 
permanganate oxidation reactions. To prevent the accumulation of these deposits in the distribu¬ 
tion system, post-filtration treatment must be applied. 

Potassium permanganate is a Class 2 Solid Oxidizer. The storage of more than 250 lbs necessitates 
special hazardous waste precautions. Potassium permanganate can be purchased in a variety of 
quantities, including 55-lb (25-kg) pails, 110-lb (50-kg) kegs, and 330-lb (150-kg) drums. The 
solids can be stored indefinitely if kept in a covered container and maintained in a cool, dry envi¬ 
ronment. Special handling and safety requirements should be employed when working with solid 
potassium permanganate, including the use of goggles, rubber gloves, and an approved NIOSH- 
MSHA dust and mist respirator. 

Careful consideration should be given to the permanganate dose estimate. Most waters contain 
substances other than As(III) that exert oxidant demand. Section 2.2.2 lists the permanganate de¬ 
mand for the stoichiometric conversion of As(III), Fe 2+ , Mn 2+ , and HS\ Permanganate reacts ag¬ 
gressively with organic materials. Permanganate may also be consumed during the regeneration of 
MnO, media. The ultimate permanganate demand is the sum of all these factors. The applied dose 
should be three times larger than the ultimate permanganate demand. 


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86 






Where: 


Eqn. 5-7 


S Mn0 4 - 3>D Mn0 4 

$Mno 4 = Permanganate Dose (mg/L as Mn) and 
D Mno 4 = Ultimate Permanganate Demand (mg/L as Mn). 

The application of potassium permanganate is straightforward. Permanganate solution is prepared 
by loading solid potassium permanganate into a storage silo. A feeder meters the permanganate 
into a dry hopper, which allows the solids to be pulled into a water stream where it dissolves. The 
permanganate solution is then stored in a solution tank until it is metered into the water to be 
treated. This process is shown in the flow diagram in Figure 5-6. For small systems looking to 
maintain simplicity, manually loading solids into a solution tank filled with water to create batch 
quantities of permanganate solution is recommended. 

Pre-engineered drum inverters (Figure 5-7) and dry feeders (Figure 5-8) are available in several 
different styles, including gravimetric weigh-belt and volumetric (hopper) type. 



Oxidized Water 
to Treatment 


Figure 5-6. Typical Permanganate Process Flow Diagram. 


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Figure 5-7. Permanganate Dry Feed System Figure 5-8. Permanganate Dry Feed System 
(Merrick Industries, Inc.). (Acrison, Inc.). 

The stock solution is then metered into the water system with the use of a small pump. The flow 
rate of solution required to meet the dose requirements are contingent upon the strength of the stock 
solution, according to Equation 5-8. 


Q-5 


MnO. 


f 


’MnO. 


^Mn0 4 ^Mn0 4 


60 


min 

"hr" 


\ 


Where: 

QMno 4 = Permanganate Metering Pump Rate (gph), 

Q = Design Flowrate (gpm), 

s Mn 0 4 = Permanganate Dose (mg/L), and 

c Mno 4 = Permanganate Stock Solution Concentration (mg/L). 


5.3 Ozone Pre-Oxidation Design Considerations 


Eqn. 5-8 


Ozone can be used in water treatment for disinfection, oxidation, and taste and odor control. Ozone 
is a gas and is created either by passing air through an electrical discharge or by irradiating air with 
UV light. The UV method is much less expensive, quite reliable, and can produce ozone in a 0.1% 
concentration. 

Careful consideration should be given to the ozone dose estimate. Most waters contain substances 
other than As(III) that exert oxidant demand. Section 2.2.3 lists the ozone demand for the stoichio¬ 
metric conversion of As(III), Fe 2+ , Mn 2+ , and HS\ Ozone will also react with TOC. The ultimate 
ozone demand is the sum of all these factors. The applied dose should be three times larger than the 
ultimate ozone demand. 


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Where: 


So 3 -3-Dq 3 


= Ozone Dose (mg/L) and 
= Ultimate Ozone Demand (mg/L). 


Eqn. 5-9 


o 3 

o 3 


To create ozone, an air stream is passed through a tube irradiated with UV light. This excites the 
oxygen (O,) molecules and causes some of them to form ozone (0 3 ). The air stream containing 
ozone is injected and mixed into the raw water, which then passes into a contactor, which provides 
time for the ozone to dissolve into the water. The mixture then flows into a de-gas separator that 
allows the un-dissolved gasses to separate to the top where they leave the separator, pass through a 
residual ozone gas destructor, and are off-gassed. The contactor and de-gas separator also provide 
time for ozone to oxidize the As(III) into As(V), which, depending on interfering reductants that 
may be present, could be as long as 2.2 minutes. Figure 59 below shows a process flow diagram for 
a typical ozonation process. 



Venturi 

Injector 



Offgas 


o 

"3 

c 

3 

co 


Oxidized Water 
to Treatment 


Figure 5-9. Typical Ozonation Process Flow Diagram. 


The ozone generator can be sized by taking the flowrate times the ozone dose as shown in the 
equation: 


Where: 





^0.2271— 



g 

mg 


min ^ 



M 0 = Ozone Mass Flow (g/h 0 3 ) 

5q 3 = Ozone Dose (mg/L) and 
Q = Design Flowrate (gpm). 


Eqn. 5-10 


Figure 5-10 shows an ozone generator that will produce up to 35 g/h (583 mg/min) of ozone. 


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Figure 5-10. Ozone Generator and Contactor (ProMinent). 

5.4 Solid Phase Oxidant Pre-Oxidation Design Considerations 


Filox-R™ is a solid, granular manganese dioxide media typically used to remove iron and manga¬ 
nese from drinking water. FiloxR™ media has also been shown to effectively catalyze the oxida¬ 
tion of As(III) to As(V) using dissolved oxygen. 

For most ground water sources, the dissolved oxygen content will be very low. Oxygen may need 
to be added depending upon the concentrations of interfering reductants. An alternative to adding 
oxygen is to increase the empty-bed contact time (EBCT) to overcome the interfering reductants. If 
oxygen addition is selected, it can be done by injecting air into the water stream using a venturi air 
injector as shown below in process flow diagram Figure 5-11. Figure 5-12 shows the schematic of 
an air injection assembly. The water and air are allowed to mix for a short period of time and then 
the undissolved gasses are removed from the water by a degassing unit. The oxygenated water then 
flows downward through a column of FiloxR™ media. 


Offgas 


Raw 

Water 



Injector 



Solid 

Phase 

Oxidant 

Column 



Oxidized Water 
to Treatment 


Figure 5-11. 


Typical Solid Phase Oxidant Arsenic Oxidation Process Flow Diagram. 


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PRESSURE REGULATING, OR 
FLOW CONTROL VALVE 

I 



Figure 5-12. Venturi Air Injector Assembly Schematic (Mazzei). 

Careful consideration should be given to the dissolved oxygen dose estimate. Most waters contain 
substances other than As(III) that exert oxidant demand. Section 2.2.4 lists the oxygen demand for 
the stoichiometric conversion of As(III), Fe 2+ , Mn 2+ , and HS. FiloxR™ may also catalyze oxida¬ 
tion with TOC. The ultimate ozone demand is the sum of all these factors. The applied dose should 
be at least ten times larger than the ultimate oxygen demand as seen in the equation below. Some 
test runs by Ghurye and Clifford with interfering reductants used as much as 65 times the stoichio¬ 
metric oxygen demand (Ghurye and Clifford, 2001). 

8 n = 10 • D n Eqn. 5-11 

U 2 U 2 

Where: 

5 q = Oxygen Dose (mg/L) and 

D 0 = Ultimate Oxygen Demand (mg/L). 

The EBCT is the other important design criteria for a solid-phase oxidant system. Tests using 
FiloxR™ were successful with EBCTs of 1.5 minutes. If oxygen was not present in 10 to 65 times 
the stoichiometric demand, EBCTs of 6 minutes were required. (Ghurye and Clifford, 2001). 

Typical hydraulic loading rates for Filox-R™ systems are 10 to 20 gpm/sft. Given this and the 
EBCT, the height of the Filox-R™ bed can be determined using the equation: 


z 


> HLR•EBCT• 


' eft ' 

J.48 gal. 


Where: 

Z = Depth of Media (ft), 

HLR = Hydraulic loading rate (gpm/sft), and 
EBCT = (Minimum) Empty Bed Contact Time (min). 


Eqn. 5-12 


Additional typical design and operating parameters for a Filox-R™ system are given in Table 5-1. 


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Table 5-1. Typical Filox-R™ Design and Operating Parameters. 

Parameter 

Value 

Units 

Bulk Density Filox-R™ 1 

114 

Ibs/cft 

Freeboard 1 

30-50% 


Filox-R™ Media 1 

>20 

in. 

Hydraulic loading rate 2 

10-20 

gprrVsft 

Empty Bed Contact Time 3 

1.5-6.0 

min. 

Minimum Backwash Flowrate 1 

12-15 

gpm/sft 


1 Recommendation by Matt-Son, Inc., Filox-R ™ Media, Form No. FXR-01. 

2 Recommendation by Matt-Son, Inc., Filox-R™ Media, Form No. FXR-06. 

3 Ghurye and Clifford, 2001. 


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5.5 Comparison of Pre-Oxidation Alternatives 


Table 5-2 provides a review of issues pertinent to the five pre-oxidation methods previously discussed. 


Table 5-2. Comparison of Pre-Oxidation Alternatives. 


Criteria 

Liquid Sodium 
Hypochlorite System 

On-Site Hypochlorite 
Generation System 

Permanganate Solution 
Feed System 

Ozone Generation 

Solid Oxidant 
System 

Safety and 
Regulatory 
Issues 

• HazMat regulations for 
safety and handling apply. 

• Potential for corrosive 
vapors in the presence of 
moisture. 

• Emergency response 
plan required with focal 
fire department. 

• Secondary containment 
required. 

• Below 1% threshold for 
hazardous classification. 

• Exempt from HazMat 
regulations. 

• No secondary 
containment requirements. 

• Solid permanganate 
poses dust and 
inhalation hazard. 

• Poisonous and 
reactive gas. 

• None. 

Space 

Requirements 

• Space requirements are 
small, assuming the 

Uniform Fire Code 
(UFC) exempt criteria 
are met. 

• Space requirements are 
large. There must be 
room for salt storage, 
brine tanks, hypochlorite 
holding tanks, electrolytic 
equipment, as well as 
instrumentation & control 
and power. 

• Space requirements 
are small. Additional 
space may be required 
for storage of solid 
permanganate. 

• Space requirements 
are smalL 

• Space 
requirements are 
small. 

Chemical 

Characteristics 

• 514 or 121/2% sodium 
hypochlorite sohitioa 
Degrades over time. 

• Decay of solution creates 
chlorate byproduct. 

• Increases pH of water 
slightly. 

• Stable sodium 
hypochlorite solution 
(0.8%). 

• Constant application 
concentratioa 

• Chlorate formation low to 

none. 

• Increases pH of water 
slightly. 

• Stable permanganate 
solution, generally 3- 
4%. 

• Reacts rapidly with 
dissolved organics. 

• Gas. 

• Very strong oxidizer. 

• Solid. 

• Requires 
dissolved oxygen 
in the water. 

Chemical 

Delivery 

• Liquid hypochlorite 
delivered by tanker truck, 
55-gal drum, or 5-gal 
pal 

• Salt delivered in 50-lb 
bags or 2000-lb totes. 

• Solid permanganate 
available in 25-kg 
pails, 50-kg kegs, and 
150-kg drums. 

• N/A 

• N/A 

Labor 

• Periodic delivery. 

• Dilution procedures. 

• Salt delivery. 

• Weekly loading of salt 
into brine tank. 

• Load dry feeder. 

• Dilution procedures. 

• N/A 

• N/A 

Operation and 
Maintenance 

• Low day-to-day O&M. 
Long-term material 
maintenance could be a 
problem because of 
corrosive effects of liquid 
hypochlorite. 

• Moderate O&M, mainly 
associated with salt 
handling. Change 
electrode cells every five 
years. 

• Low day-to-day 

O&M for automated 

systems. 

• Stains everything 
purple. 

• Low day-to-day 
O&M. 

• Low day-to-day 
O&M. 

Off- Normal 
Operation 

• A temporary bleach 
solution can be mixed in 
the storage tank. 

• A temporary bleach 
solution can be mixed in 
the day tank. 

• N/A 

• N/A 

• N/A 

Community 

Relations 

• HazMat signage required. 

• No HazMat regulations. 
Hydrogen byproduct 
vented to atmosphere. 

• N/A 

• N/A 

• N/A 


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Section 6 

Sorption Process Design Considerations 

This section describes the design of sorptive processes, including AA, modified AA, IBS, and IX. 
For reasons previously cited, the discussion about AA, modified-AA, and IBS are restricted to non- 
regenerable applications. Conversely IX is most economically feasible when used in a regenerable 
process. 

6.1 Process Flow 


Despite the availability of several different types of sorptive treatment processes, the overall treat¬ 
ment approach for each is similar. Pre-treatment can consist of oxidation, to convert As(III) to 
As(V), and pre-filtration stages when turbidity is high, as well as optional pH adjustment and pre¬ 
filtration backwash. Next, the water is fed through a column packed with sorptive media. Post¬ 
treatment consists of an optional pH re-adjustment stage and some media have an option for regen¬ 
erating the media. Typically, the entire process is carried out under pressure. Figure 6-1 shows a 
typical sorption treatment process while Figure 6-2 shows the same flow diagram with the optional 
media regeneration and pH adjustment and re-adjustment. Dashed lines and boxes indicate op¬ 
tional streams and processes. 


Raw 

Water 



Treated 

Water 


Backwash 

Waste 


Figure 6-1. Sorption Treatment Process Flow Diagram w/o pH Adjustment and Regeneration. 


Raw 

Water 


Oxidant — 


Acid- 7 


Pre- 

Oxidation 



\ Pre- 
| Filtration 


Sorptive 

Treatment 


Base —•, 


* 

pH 

Re-Adjustment 


Treated 

Water 


Backwash Waste Regenerant 

Waste (IX Only) (IX Only) 


Figure 6-2. Sorption Treatment Process Flow Diagram w/ pH Adjustment and Regeneration. 


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Pre-filtration is strongly recommended when the source water turbidity is above 0.3 NTU. Sus¬ 
pended solids in the feed water can clog sorption sites and impair process hydraulics. One prefiltration 
option for smaller systems is backwashable cartridge filters. 

The performance of AA treatment is highly pH-sensitive. Treatment conducted under acidic condi¬ 
tions (pH 5.5-6.0) can be expected to produce run lengths 5 to 20 times longer than treatment 
conducted under natural pH conditions. As a result, in the decisions trees in Section 3, conven¬ 
tional AA is only recommended over IBS when the pH is naturally low or the system is willing to 
adjust the pH below 6.0. In most cases, pH adjustment will require chemical addition of a strong 
acid, such as sulfuric (H 2 S0 4 ) or hydrochloric (HC1) acid. Dose requirements depend on the back¬ 
ground pH and buffering capacity of the water. 

6.2 Column Rotation 

Sorption processes are conducted using two or more columns in series. The first column in the 
treatment process is referred to as the roughing column, and the last sorption column is referred to 
as the guard column. Frequently, there is an additional column on standby. The roughing column 
serves as the primary arsenic removal column. The guard column is intended to capture arsenic 
breakthrough as soon as it occurs from the roughing column. 

The columns are operated in this manner until arsenic breakthrough of the roughing column occurs, 
which is detected by periodic grab samples. Breakthrough is generally defined as the time when the 
effluent arsenic concentration is equal to 50% of the feed water arsenic level. However, this num¬ 
ber can be adjusted after piloting or operation to optimize the economics of the process. At this 
point, adsorptive sites on the roughing column have become saturated and the column should be 
taken off-line for media replacement or regeneration, after which it is placed in standby mode to 
wait for the next column rotation. The guard column is then promoted to the roughing column 
position and the standby column becomes the guard column in the series. Figure 6-3 illustrates 
how the columns’ positions are rotated between roughing, guard, and standby operation modes. 

The number of columns to be placed in series depends on the estimated lifetime of each column and 
the desired monitoring and media change-out or regeneration frequency. IX processes operating 
with sulfate in the feed may have a sulfate roughing column at the head of the operation to remove 
sulfate before arsenic is removed by the arsenic roughing column. 

Typically two parallel process trains are used. This provides operational redundancy and, by stag¬ 
gering their operation, chromatographic peaking may be reduced. 


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96 



Normal Operation Mode 


Feed Water 



Distribution 

System 


Regeneration/Replacement Mode 



Replacement 

Media 


Distribution 

System 


Figure 6-3. Sorption Column Operation Modes. 

6.3 Sorption Theory 


To understand operation of sorption processes, it is important to understand fundamental ion ex¬ 
change theory. An important consideration in sorption processes is the mass transfer zone (MTZ), 
which can be viewed as a wave or a zone of activity (i.e., non-equilibrium between liquid and 
media phases) for a particular contaminant. As depicted in Figure 6-4, the MTZ also represents the 
front of the exhaustion zone for a particular contaminant. Exhaustion zones and MTZ waves are 
typically considered for the target contaminant (i.e., arsenic) and any species that have a higher 
exchange affinity for the media. Arsenic must compete with other anions for exchange sites ac¬ 
cording to the selectivity sequence for the particular media (see Section 2). Previously sorbed 
arsenic can be displaced by anions of higher selectivity. Exhaustion and MTZs order themselves 
according to the selectivity sequence, as illustrated in Figure 6-4. Other sorbed contaminants, such 
as carbonate (C0 3 2 ) and nitrate (N0 3 ), would be present further down from the As(V) MTZ. 


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Resin Loaded (%) 


M Exhausted 

Partially Loade d Media 
(MTZ) 



Fresh Media 




Figure 6-4. Multi-Component Ion Exchange. 

6.3.1 Non-Regenerated Sorption Processes 

For the purpose of this Handbook, processes utilizing AA, modified-AA, or IBS media are 
referred to as non-regenerated sorption treatment. These technologies are most applicable 
to small utilities when used as a one-time application with subsequent media disposal and 
replacement. 

Processes utilizing conventional AA function best when the solution pH is less than 6.0. At 
this pH, the hydroxide (OH ) concentration is less than 0.2 mg/L. Since this is at least an 
order-of-magnitude less than the arsenic concentration, hydroxide provides little competi¬ 
tion against arsenic for exchange sites. There are several types of modified-AA that have 
demonstrated enhanced arsenic removal performance under natural pH conditions (6.0-9.0) 
but these were not designated as BATs by the USEPA when the rule was promulgated. 

IBS treatment has been described as chemisorption (Selvin et ah, 2000), which is typically 
considered to be irreversible. Therefore, although phosphate and arsenic compete for sorp¬ 
tion sites, neither has the ability to displace the other. In this instance, there is a single 
exhaustion zone and MTZ comprised of both As(V) and phosphate contaminants. 

6.3.2 Ion Exchange Processes 

As(V) can be removed through the use of SBA in either chloride or hydroxide form, al¬ 
though the former is more commonly used for drinking water applications. The expense 


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and low capacity of IX resin generally renders it uneconomical for one-time application and 
disposal. Instead, periodic regeneration should be applied to restore the exchange capacity 
of the resin. 

Figure 6-4 illustrates a resin-phase loading profile down an IX column for treatment of 
hypothetical natural water containing arsenic and sulfate. As arsenic is exchanged with 
anions on the SBA, the arsenic band develops and its MTZ moves downward. The same 
phenomenon is true for sulfate ions. However, because of its higher exchange affinity, 
sulfate anions displace the arsenic, thereby forcing the arsenic-exhausted region and the 
arsenic MTZ downward further. 

An important consideration in the application of IX treatment is the potential for chromato¬ 
graphic peaking of nitrate (NOy) and nitrite (NO,). These contaminants pose an acute 
health risk, and as such are regulated under the SDWA with primary MCLs of 10 mg/L (as 
N) and 1 mg/L (as N), respectively. According to the selectivity sequence provided in 
Section 2.3.1, nitrate and nitrite will also replace chloride on exchange sites, although with 
less preference than As(V) or sulfate. As a result, the region of nitrate and nitrite activity 
will reside further down the column (relative to the activity of sulfate and As(V)), as illus¬ 
trated in Figure 6-5. These species will chromatographically peak before As(V), and this 
peaking could produce water that does not meet the aforementioned MCLs. Utilities with 
source water with measurable quantities of nitrite or nitrate should be aware of this phe¬ 
nomenon and plan column operation to avoid this occurrence. 



Exhausted Media 

Partially Loade d Media 
(MTZ) 

Fresh Media 


S0 4 2 ' HAs0 4 2 ' N0 3 ' N0 2 




Figure 6-5. Activity of Nitrate and Nitrite During Ion Exchange. 


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The removal of carbonate (C0 3 2 ) by IX resin can also lead to a pH drop of 0.5 to 1.0 units, 
particularly at the beginning of a run. This impact can be minimized by post-treatment 
addition of soda ash or caustic soda or by sequencing the regenerative cycles of parallel 
process trains. Pilot testing is recommended to evaluate the impact on pH for the specific 
water in question. 

6.4 Process Design & Operational Parameters 

Design and operational parameters for sorption treatment processes vary significantly depending 
on the specific technology chosen, and to a lesser degree on the media type. The most appropriate 
way to identify the optimal engineering parameters for a particular treatment application is to con¬ 
duct on-site pilot column studies with the media of interest. 

Regenerable IX processes involve three operating modes: (1) Loading; (2) Regeneration; and (3) 
Rinsing. Loading can be conducted with flow in either the downward or upward direction, al¬ 
though the former is more common in water treatment applications. Once the column is fully 
loaded it should be taken off-line. The next step is regeneration with concentrated brine for chlo¬ 
ride-based SBA, which can be conducted in either the downward or upward direction. The latter 
case is generally more effective, although care must be taken to prevent fluidization of the media. 
Prior to returning the column to service, water rinsing should be conducted to displace regenerant 
solution from the column. Slow rate and fast rate rinsing should be conducted in sequence, with 
each displacing about 2-3 bed volumes of solution per column. 

Table 6-1 details key design and operational parameters for AA, IBS, and IX processes. As de¬ 
scribed in Section 2, non-regenerable AA and IBS process are recommended for small utilities. 
Therefore, rinsing and regeneration data is only provided for ion exchange processes. 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


100 



Table 6-1. Typical Sorption Treatment Design and Operating Parameters. 

Parameter 

IX 

AA 

IBS 

Units 

Media Bulk Density 

40-44 

40-47 

72-75 

Ibs/cft 

Minimum Column Layers 

Freeboard 

90% >' 2 

50% 3 

50% 

- 

Media 

36-60 2 

36-60 3 

32-40 

in. 

Operating Conditions 

Hydraulic Loading Rate 

8-12 2 

4-9 3 

5-8 

gpm/sft 

Empty Bed Contact Time 

1.5-5 

5 3 

5-10 

min. 

Downflow Pressure Drop 4 

0.7-1.3 2 

0.1 6 

N/A 

psi/ft 

Maximum Pressure Differential 

14 

5 

3.5 

psi 

Backwash Conditions 

Backwashing Flow Rate 

3-4 2 

7 3 

- 

gpm/sft 

Backwashing Duration 

5-20 2 

10 3 

- 

min 

Regeneration Conditions 1 

Brine Strength 

6-10 2 

- 

- 

wt% 

Downflow Rate 

2-6 

- 

- 

gpnVsft 

Regenerant Volume 

20 2 

- 

- 

gal/cft resin 

Rinsing Conditions 

Slow Rinse Rate 

0.4-4 

- 

- 

gpnVsft 

Fast Rinse Rate 

2-20 

- 

- 

gpm/sft 

Displacement Requirements 

4-6 

- 

- 

bed volumes 


1 This will be very resin specific. Check with the resin manufacturer before design. 


2 Rubel, 2001 a Draft. 

3 Rubel, 2001b Draft. 

4 This depends on temperature, type of media, and hydraulic loading rate. 

5 For strong base anion exchange resin at 70°F and 10 gpm/sft. 

6 For AA at 2 gpnVsft. 

N/A - Not Available. 


6.5 Column Design 

The vessels should be made from typical, well-known materials of construction such as carbon 
steel or fiberglass and must be NSF approved. The vessels should have distribution and collector 
systems that provide a uniform distribution of fluids during all phases of the operation. More detail 
on these accessories is provided in Section 7. Also, it is advisable to install sight-glasses in order to 
check resin levels. 

Columns placed in series are referred to as a treatment train. The utility should evaluate the number 
of parallel treatment trains based on the desired redundancy and state design standards. Figure 6-6 
shows a commercially available multiple-column IX treatment train. 


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Figure 6-6. Ion Exchange System (Tonka Equipment Company). 

6.5.1 Column Diameter 

Once the number of parallel treatment trains has been established, column diameter can be 
calculated based on the recommended hydraulic loading rate of the particular media and the 
design flowrate. Hydraulic loading rate is the flowrate per unit of cross-sectional area and 
is proportional to the linear velocity of the fluid through the bed. Recommended maximum 
hydraulic loading rates are provided in Table 6-1. Column diameter (D) can be calculated 
using the equation: 


Where: 

D 

Q 

n P 

HLR 


7i • n p • HLR 

= Column Diameter (ft), 

- Design Flowrate (gpm), 

= Number of Parallel Treatment Trains, and 
= Hydraulic loading rate (gpm/sft). 


Eqn. 6-1 


The benefits of lower hydraulic loading rates include a sharper MTZ and potentially better 
media utilization. However, a lower hydraulic loading rate also translates into a larger 
column footprint. 


Consider an example where IX will be used to treat a design flowrate of 70 gpm. The utility 
has decided to provide no parallel treatment trains. Based on a recommended maximum 
hydraulic loading rate of 10 gpm/sft, the column diameter should be 3 feet. 



Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


102 






= 3 ft 


D = 


4-70 gpm 


\0.5 


7t • 1 -10 gpm/sft 


6.5.2 Column Height 

The depth of sorptive media required can be calculated based on the selected hydraulic 
loading rate and consideration of the minimum empty bed contact time. Values of EBCT 
are provided in Table 6-1. 


Z 


>HLR EBCT 


' eft ' 
,7-48 gal. 


Where: 

Z = Depth of Sorptive Media (ft), 

HLR = Hydraulic loading rate (gpm/sft), and 
EBCT = (Minimum) Empty Bed Contact Time (min). 


Eqn. 6-2 


Returning to the previous example, suppose the specific resin selected had a minimum 
EBCT of 3 minutes. The total depth of sorptive media required for the primary treatment 
columns would be 4 feet. 


z = 


10 


gpm 

sft 


• (3 min)- 


eft 


7.48 gal 


= 4 ft 


The depth of sorptive media (Z) should then be used in conjunction with the column free¬ 
board to determine column height. For ease of change-out, all columns should be sized 
similarly. 


H = Z-(l + F) 


Where: 

H = Column Height (ft), 

Z = Depth of Sorptive Media (ft), and 
F = Freeboard Allowance (% expressed as a decimal). 


Eqn. 6-3 


For the previous example, if the freeboard requirement was 50% of media depth, the col¬ 
umn height should be 6 feet. 


H = (4 ft)-(1 + 0.5) =6 ft 

Therefore, for this particular example, the design should include a single treatment train 
consisting of three columns (i.e., roughing, guard, and standby). All columns should be 3 
feet in diameter by 6 feet tall and contain 4 feet of media. The process flow diagram for this 
example is provided as Figure 6-7. 


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Roughing 

Column 


Guard 

Column 


Standby 

Column 


Pre-Oxidized 
Raw Water 


•O—CH o 


► 


Treated 

Water 


Figure 6-7. Process Flow Diagram for Example Problem. 

The following constraints should also be considered: 

• Small column aspect ratios (i.e., H:D <1) can lead to flow maldistribution. 

• Large column heights can lead to excessive pressure drop. 

• The available building footprint. 

• The available building height. 

6.6 Media Replacement Frequency 


It is advantageous for a utility to obtain a rough estimate of the optimal operating time until media 
exhaustion occurs. This is important for establishing an appropriate O&M and monitoring sched¬ 
ule. The optimal filter run time until media exhaustion can be calculated as: 


x = BV e • EBCT • 


f hr 
^ 60 min 


\ 

) 


Where: 

x = Optimal Filter Run Time (hr), 

BV e = Number of Bed Volumes to Exhaustion, and 
EBCT = Empty Bed Contact Time (min). 


Eqn. 6-4 


The roughing column should be operated until 50% arsenic breakthrough occurs. Therefore, the 
actual filter run time will be less than the calculated optimal filter run time (t). The deviation will 
depend on the efficiency of the sorption/exchange process and the width of the MTZ. 

Consider an example where the estimated lifetime of a particular combination of media and raw 
water was 1,357 BV. If the columns are sized to provide an EBCT of 3 minutes, the optimal run 
time until media exhaustion is 68 hours. 


x = (l ,357 Bed Volumes) - (3 min)- 


r hr 
60 min 


A 

= 68 hr 


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6.7 Regeneration of Ion Exchange Resin 


IX resins are essentially unusable for arsenic removal unless they can be efficiently regenerated. 
Because of the high selectivity of SBA for sulfate (S0 4 2 ), the exchange capacity would be ex¬ 
hausted within a few days for many natural waters. The cost of the virgin resin is far too great to 
dispose of it at that time. 

Chloride-based SBA can be regenerated with concentrated brine (1-5 mole/L) in either the up flow 
or downflow mode. The more concentrated the regenerant solution, the greater the fraction of the 
bed that is regenerated. It should be noted, however, that regeneration efficiencies are generally 
less than 100%. Therefore, successive runs can be expected to be slightly shorter in duration. 

Utilities should consider the size of the brine holding tank, as they are typically much larger than 
the IX columns themselves. Based on previous studies (AwwaRF, 2000), roughly 4 BVs of spent 
brine are produced per regeneration. The regeneration duration can be calculated as: 

( 4BV ) Eqn. 6-5 

Where: 

t R = Regeneration Duration (min), 

Z = Depth of Sorptive Media (ft/B V), and 
G r = Regeneration Flux (gpm/sft). 

Following regeneration, this brine can either be disposed of via indirect discharge (assuming local 
TBLLs are met) or stored for recycle. In the case of recycle, it may be necessary to add salt to bring 
the strength of the brine back to the range 15 mole/L. 

For a conventional IX process, spent regenerant will contain arsenic and sulfate in a ratio approxi¬ 
mately corresponding to their relative concentration in the raw water. If the water contains a mod¬ 
erate amount of competing ions, it is possible that the brine waste will contain less than 5.0 mg/L of 
arsenic, and thus will not exceed the TC values. However, in most instances, the liquid waste 
stream will contain more than 5.0 mg/L of arsenic. This will force utilities to consider disposal and 
waste treatment options. If indirect discharge to a local POTW is the waste disposal method cho¬ 
sen, a spent brine holding tank may be required in order to slowly release the spent brine to the 
POTW. 

Rinsing with water is typically conducted after regeneration to flush out residual brine and prepare 
the column for normal operation. Generally 4 to 6 BV of rinse water are used per regeneration. 
This waste may be added with the brine waste being sent to the POTW. 

IX resin typically lasts 4-8 years before chemical and mechanical degradation necessitates media 
replacement. 


l R “ 


7.48 


gal 

eft 


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6.8 Waste Handling Systems 


This section addresses three types of waste: backwash water from pre-filters, spent regenerant, and 
spent media. 

The two most probable methods for disposal of backwash water from pre-filters are indirect dis¬ 
posal through a POTW or by settling the solids, recycling supernatant, and sending the solid sludge 
to a landfill. 

Regarding brine used in IX regeneration, there are two waste disposal options. Spent brine that 
contains less than 5.0 mg/L of arsenic can either be disposed of via indirect discharge or treated on¬ 
site. The feasibility of indirect discharge of regenerant waste will be dictated by local TBLLs for 
TDS. The concentration of TDS in the spent regenerant can be approximated as: 


Where: 

r 

TDS 

M Brine 


TDS 


58.4 


g NaCl 
mole 


M Brine 


= Concentration of Total Dissolved Solids (g/L) and 
= Brine Molarity (mole/L). 


Eqn. 6-6 


When indirect discharge is not an option, the system must deal with the waste on-site. The most 
common approach for treating brine waste (containing less than 5.0 mg/L of arsenic) is chemical 
precipitation with iron-based salts and subsequent solids thickening. Thickening can be conducted 
using a settling basin, or for more rapid results, mechanical dewatering equipment. The brine 
decant can then be sent to an evaporation pond. 

Spent brine used in the regeneration of arsenic-laden resin may be classified as hazardous. There¬ 
fore, manipulating the chemical form of the waste on-site constitutes treatment of a hazardous 
waste, which has extensive permit and cost implications. As a result, when the brine waste stream 
contains over 5.0 mg/L of arsenic, indirect discharge to a POTW is considered the only viable 
option for small utilities. When this option is unavailable, on-site regeneration of arsenic-laden 
resin should not be performed. Rather, the resin should be disposed of at a municipal solid waste 
landfill and replaced with fresh resin. 

The appropriate disposal method for spent resin is dependant on the results of the TCLP, as de¬ 
scribed in Section 1. 


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Section 7 

Pressurized Media Filtration Process 

Design Considerations 


This section describes the design of a typical pressurized granular-media filtration system includ¬ 
ing sand filtration and iron and manganese oxidation/filtration systems. Although the following 
information specifically describes a pressurized greensand filter, it can be applied to any pressur¬ 
ized granular media filtration system. 

7.1 Process Flow 


In a typical media filtration process, seen in Figure 7-1, the raw water is first put through a pre¬ 
oxidation step. Dashed lines and boxes indicate optional streams and processes. If the preoxidant 
is chlorine, potassium permanganate, or ozone, the As(III) and any natural iron will be oxidized to 
As(V) and Fe III respectively. If, however, aeration (aeration tower) is used for iron oxidation, the 
air oxidation process will not oxidize As(III) to As(V) and the addition of a chemical preoxidant 
would be required. If greensand is being used as the filter media, potassium permanganate and 
chlorine also provides the oxidant for the continuous regeneration of the greensand media. 


Raw Water 



Backwash 

Waste 


Treated 

Water 


Figure 7-1. Typical Media Filtration Process Flow Diagram. 

It should be noted that, although greensand can be regenerated in either batch or continuous meth¬ 
ods, only the continuous regeneration method has been shown to also oxidize the As(III) to As(V) 
so that arsenic can be removed. Therefore, under most circumstances, only the continuous regen¬ 
eration method is recommended for arsenic removal. 

After pre-oxidation, a coagulant addition step may be necessary if the iron concentration or the 
Fe: As ratio is low. Next, the water is passed through filters containing granular media before being 
sent to the distribution system. Typically, three or more filters are provided in parallel. 


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Media filters are operated in three different modes: (1) Filtration; (2) Backwash; and (3) Filter-To- 
Waste (FTW). In the operating mode, all filters are fed in parallel with flow in the downward 
direction. The effluent is sent to the distribution system as shown in Figure 7-2. 

After some time of operation, solids captured by the filtration media will impede the flow and 
increase the differential pressure across the filter. To restore hydraulic capacity, the filter will have 
to be backwashed. The backwash flow is in the upward direction, which fluidizes the granular 
media and washes the accumulated solids out of the filter. In some instances, air scouring is con¬ 
ducted prior to fluid backwashing. Air scouring bubbles large volumes of air upward through the 
filter. This assists in breaking apart conglomerates of filtered material, allowing the subsequent 
fluid backwash to more easily remove the captured solids. An air scour also reduces the volume of 
backwash waste that is generated. 



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After backwashing, the media is allowed to settle and downward flow is reinstated with the filter 
effluent going to waste. This re-stratifies the column, setting it up for operation. It also reduces the 
amount of particulate matter that gets into the distribution system. After the FTW mode, the filter 
is returned to standard operation. 

7.2 Process Design & Operational Parameters 

Table 7-1 lists design and operational parameters typical of media filtration systems. 


Table 7-1. 

Typical Greensand Column Design and Operating Parameters. 

Parameter Value 

Units 

Media Bulk Density 

Anthracite Media 1 

50 

Ibs/cft 

Greensand Media 2 

85 

lbs/cft 

Garnet Media 3 

140 

Ibs/cft 

Support Gravel 4 

100 

Ibs/cft 

Column Layers 

Freeboard 1,2 

50% 

of Anthracite and Greensand 

Anthracite Media 5 

12-24 

in. 

Greensand Media 6 

15-24 

in. 

Garnet Media 3 

4 

in. 

Support Gravel 4 

18-30 

in. 


Operational Parameters 


Hydraulic loading rate 7 8 

3-5 

gpm/sft 

Max Pressure Differential 

8-10 

psi 

Backwash Parameters 

Minimum Backwash Flowrate 2 

12 

gpm/sft 

Backwash Duration 

15 

min. 

Backwash Frequency 

1-7 

days 

Bed Expansion 2 

40% 

minimum 

Air Scouring Rate 

0.8-2.0 

scfrn/sft 

Filter-to-Waste Parameters 

FTW Hydraulic loading rate 

3-5 

gpnVsft 

FTW Duration 

5 

min. 


1 Recommendation by Clack Corporation, Anthracite, Form No. 2354. 

2 Recommendation by Clack Corporation, Manganese Greensand, Form No. 2349. 

3 Recommendation by Clack Corporation, Garnet, Form No. 2355. 

4 Recommendation by Clack Corporation, Filter Sand and Gravel, Form No. 2352. 

5 Clack Corporation, Anthracite, Form No. 2354 recommends 10-18 for multimedia filters but may need to be higher 
depending on iron concentrations. 

6 Clack Corporation, Manganese Greensand, Form No. 2349 recommends 30" but can be lower if used with 
continuous regeneratioa 

7 Clack Corporation, Manganese Greensand, Form No. 2349 recommends 3-5 gprrVsft with 8-10 gpm/sft intermittent 
flow possible. 

8 Under some circumstances, continuous flowrates of 10 gpm/sft are possible. 


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7.3 Filter Design 


Typically, granular-media pressure filters have multiple layers of media selected to maintain a coarse- 
to-fine grading from the top to bottom of the filter. The coarse, upper layer provides rough filtration 
and the bulk of the particulate retention while the fine, lower layer provides superior filtration. This 
scheme allows for longer runs times while maintaining filtration quality. A typical oxidation/filtra¬ 
tion filter is shown in cross-section in Figure 7-3. 


Filter Influent 
Backwash Effluent 



Freeboard 


Anthracite 


Greensand 



Filter Garnet 
Support Gravel 


Distribution Laterals 



Distribution Header 


► Filter Effluent 
Backwash Influent 


Figure 7-3. Schematic of a Vertical Greensand Pressure Filter. 

In the manganese greensand oxidation/filtration process, the primary layer in the filter is made of a 
media that catalyzes iron and manganese oxidation, promotes its precipitation, and filters out the 
precipitate. For optimum arsenic removal, continuous chemical preoxidation with either potas¬ 
sium permanganate or chlorine is recommended. Arsenic is removed by the co-precipitation with 
the iron and, to a lesser degree, the manganese. Greensand, glauconite sand coated with a thin layer 
of MnO„ is the most common of these types of materials. 

Because greensand is very fine (16-60 mesh) it is susceptible to being overloaded with solids. To 
reduce the solids loading on the greensand a layer of filter coal such as anthracite is put on top. This 
layer also provides an area for the iron floe to coagulate. Because of anthracite’s low density, the 
filter coal will naturally stratify as the top layer after backwash. 

In order to keep the greensand from being slurried out the under-drain, a layer of filter garnet is 
placed below it. This filter garnet has a particle size of 8-12 mesh and a density almost 50% greater 
than the greensand. This puts the filter garnet below the greensand after stratification. 


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The bottom layer is support granite, which allows the water to flow easily into the lower distribu¬ 
tion system and exit the filter. Because of its larger size, the support granite is not fluidized during 
backwash. Instead, it assists in distributing the backwash flow evenly throughout the filter. 

When the media is backwashed, it will expand 30% to 50%. To accommodate this, the filter is 
designed with freeboard. Freeboard is the amount of space in the filter between the upper layer of 
media and the upper distribution manifold. The height of this freeboard is dependent on the height 
of media but is generally 40-50% of the settled height of the media that undergoes fluidization (i.e., 
anthracite and greensand in the case of a greensand filter). 

Every filter will have an upper and lower distribution manifold. The upper manifold distributes the 
influent and collects the backwash water. The lower manifold collects filtered water and distributes 
backwash water. There are numerous designs for these distribution manifolds. Smaller diameter 
filters may have a distribution plate or a hub-lateral design shown in Figure 7-4. Larger diameter 
columns may have a header-lateral design, shown in Figure 7-5. The header-lateral design gives a 
more even distribution of the flow, which is much more important for the lower manifold, as flow 
distribution directly affects the effectiveness of the backwash. 



Figure 7-4. Hub-Lateral Distribution System (Johnson Screens). 



Figure 7-5. Header-Lateral Distribution System (Johnson Screens). 

Typical media filtration installations include several filters in parallel. This allows one to be taken 
offline while the others continue to work. It also allows the other filters to provide the backwash 
water necessary to backwash a single filter. Figure 7-6 shows one potential valving arrangement 
that allows the use of multiple filters. Figure 7-7 and Figure 7-8 show pictures of commercially 
available pressurized media filters. 


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Inlet 



Figure 7-6. Multiple Media Filter Setup. 



Figure 7-7. Pressurized Media Filter (USFilter). 


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Figure 7-8. Pre-Engineered Arsenic Filtration System (Kinetico). 

7.3.1 Filter Diameter 

The primary design variable for the granular media filters is the hydraulic loading rate. This 
is the flowrate the filters handle per horizontal cross-sectional area of media. Typical hy¬ 
draulic loading rates for greensand filters range between 3 and 5 gpm/sft, although, under 
some circumstances, greensand filters can be successfully operated at hydraulic loading 
rates as high as 10 gpm/sft. Using this information, the number of filters, and the maximum 
flowrate for which the filters are designed (i.e., design flowrate), the filter diameter can be 
calculated using Equation 7-1. 


Where: 

D 

Q 

n P 

HLR 


7i • n P • HLR 

= Column Diameter (ft), 

= Design Flowrate (gpm), 

= Number of Parallel Treatment Trains, and 
= Hydraulic loading rate (gpm/sft). 


Eqn. 7-1 


For the example of 3 parallel filters designed to treat a maximum of 300 gpm of water at a 
filter hydraulic loading rate of 5 gpm/sft, the filter diameter should be 5 feet. 


D = 


' 4-300 gpm 


s0.5 


71-3-5 gpm/sft 


= 5ft 


7.3.2 Media Weight 

The weight of each media layer can be calculated using the following equation: 



71-D 2 -hj pj 

4 


Eqn. 7-2 


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Where: 

W. = Weight of Media Layer j (lbs), 

D = Column Diameter (ft), 
h. = Height of Media Layer j (ft), and 

p j = Bulk Density of Media j (lbs/cft). 

For the previously calculated 5ft filters, using 1 ft of anthracite, 2.5 ft of greensand, 0.25 ft 
of filter garnet, and 2 ft of support granite, the media weights per filter are 982 lbs of anthra¬ 
cite, 4,172 lbs of greensand, 687 lbs of filter garnet, and 3,927 lbs of support granite, respec¬ 
tively. Typical densities for each of the media can be found in Table 7-1. 

7T • (5 ft) 2 • (2.5 ft)- (85 lbs/cft) , 

W Gr eensand = —- —-— —- ---- = 4,172 lbs of greensand (per filter) 

7.4 Waste Handling System Design 

Both the backwash water and the FTW water from granular media filtration processes pose dis¬ 
posal issues. The backwash flowrate can be calculated using the equation: 


Qbw -~T ) 2 g bw 

Where: 

Q bw = Backwash flowrate (gpm), 

G bw = Backwash flux (gpm/sft), and 
D = Column Diameter (ft). 


Eqn. 7-3 


The FTW flowrate is typically the same as the flowrate used in the filtration mode. Therefore, the 
volume of wastewater produced by the backwash and FTW modes can be calculated using the 
equation: 


Where 

V 


ww 

Qbw 

BW 

Q 

m 


V 


TW 


v ww - Qbw -t Bw + —-t 

n P 


FTW 


= Volume of Wastewater (gal), 

= Backwash Flowrate (gpm), 

= Backwash Duration (min), 

- Design flowrate (gpm), 

= Number of Parallel Treatment Trains, and 
= Filter-To-Waste Duration (min). 


Eqn. 7-4 


For example, assume the same 3-filter system as before (5-foot diameter, 300 gpm design flowrate, 
and 5 gpm/sft hydraulic loading rate) has a backwash flux of 12 gpm/sft, a backwash time of 15 
minutes, and a FTW time of 5 minutes. The required backwash flowrate is then 236 gpm/filter and 
the wastewater volume created is 4,040 gallons per backwash per filter. 


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Qbw (5 ft) 2 - 12^ 
4 sft 


= 236 gpm (per filter) 


V 


ww 


236 


gpm 

Filter 


15- 


min 


Backwash 


'i 300 gpm v 
A 3 Filters 


min 


\ 


Backwash 


= 4,040 


gallons 


Filter - Backwash 


The wastewater can be disposed of in several different ways. The two most probable methods are 
indirect disposal through a POTW or by settling the solids and recycling the supernatant and send¬ 
ing the solids to a landfill. 

In the indirect discharge through a POTW, a holding tank may be desired to eliminate the surging to 
the POTW system. In the liquid recycle/solids disposal method, a settling tank or basin is required. 
The holding basin or tank should be sized to hold at least two backwash/FTW cycles. In the above 
example, this leads to an 8,100 gallon tank. 

7.5 Coagulant Addition System Design 


The efficiency of arsenic co-precipitation to iron floe may vary depending on the concentration of 
iron and the iromarsenic ratio. Optimal performance is obtained with an iromarsenic mass ratio of 
at least 20:1. If the raw water does not meet these two parameters, iron addition may be required to 
provide enhanced coagulation. Ferric chloride (FeCl 3 ) is commonly available for use in potable 
water systems and can be obtained as a 38wt% liquid. The volumetric flowrate of ferric chloride 
solution required to meet a predetermined dose rate can be calculated with Equation 7-5. 


Where: 

QFeCl 3 

Q 

S FeCl 3 

C FeCl 3 

PFeCl 3 


Q' 5 FeCl 3 

QFeCl 3 =- “ 

'-'FeCl 3 PFeCl 3 


f 

0.003785 

V 


kg-mL 
mg • gal ^ 


= Ferric Chloride Metering Pump Rate (mL/min), 

= Design flowrate (gpm), 

= Ferric Chloride Dose (mg/L), 

= Ferric Chloride Stock Solution Concentration (wt%), and 
= Density of Ferric Chloride (kg/L). 


Eqn. 7-5 


For example, if the design flow rate of water to be treated was 300 gpm and the water needed an 
additional 1.0 mg/L of iron, a 38-wt% solution of ferric chloride with a density of 1.42 kg/L could 
be added to the water at a rate of 6.1 mL/min to provide the required iron. 


(300 gpm)- (l mg/L) 
gFeCl3 (0.38)-(1.42 kg/L) 


f 

0.003785 

V 


kg • mL 
mg • gal ^ 


= 2.1 mL/min 


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The required storage capacity for the ferric chloride solution can be calculated using Equation 7-6. 


Where: 

V 

Q 

S FeCl 3 

t 

C FeClj 
PFeClj 


V = 


Q tS FeCl 3 
C FeCl 3 PFeCl 3 


f 

0.00144 


kg ■ min N 
mg d j 


= Storage Volume (gal), 

= Design flowrate (gpm), 

= Dose Rate of Ferric Chloride (mg/L), 

= Storage Time (days), 

= Ferric Chloride Stock Solution Concentration (wt%), and 
= Density of Ferric Chloride (kg/L). 


Eqn. 7-6 


Using the same example and specifying 14 days of ferric chloride storage, the required storage 
volume would be 32.6 gallons. 


y _ (300gpm) - (l4 days) - (l mg/L) 
(0.38)-(1.42 kg/L) 


0.00144 


V 


kg • min 
mgd 


= 11.2 gal 


A generalized flow diagram for a ferric chloride chemical addition system is shown in Figure 7-9. 
The ferric chloride should be stored in a tank made of either fiberglass-reinforced polyester or 
rubber-lined steel. A flow meter installed along the main water line is used to pace the addition of 
ferric chloride to the water flowrate. An isolation valve and check valve are used in the connection 
to the water line. After the ferric chloride addition, the water is mixed with an inline mixer and the 
dosed water is sent to the filters. 



Water to 
Filters 


Ferric 

Chloride 

Storage 


Figure 7-9. Ferric Chloride Addition Flow Diagram. 


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Section 8 
Point-Of-Use Treatment 


POU devices were approved as SSCTs for meeting the revised arsenic MCL. POU devices are 
attractive for removing contaminants that pose (solely) an ingestion risk, as is the case with arsenic. 
This is because a very small fraction of the total water supplied to a given household is ultimately 
consumed. In most cases, the POU unit is plumbed into the kitchen faucet. As such, the kitchen tap 
would be the only source from which water should be collected for consumption. 

The primary advantage of employing POU treatment in a small system is reduced capital and treat¬ 
ment costs, relative to centralized treatment. On the downside, however, it is the utility’s responsi¬ 
bility to maintain equipment. Therefore, these programs generally incur higher administrative and 
monitoring costs to make sure that all units are functioning properly. POU programs are an eco¬ 
nomically viable alternative to centralized treatment for systems serving up to 500 people. 

Another downside is that the media or membranes used in POU treatment devices may be suscep¬ 
tible to microbial colonization. Higher levels of bacteria have been found in the finished water 
produced by some POU treatment devices, particularly those that incorporate an activated carbon 
element, than in the corresponding untreated water. Although no illnesses have been reported as a 
result of the use of these treatment devices, the health effects of these bacteria are still unknown. 
Therefore, additional monitoring and post-treatment disinfection may be required to ensure cus¬ 
tomer safety, increasing overall costs. 

The primary criteria for selecting an appropriate POU treatment device are arsenic removal perfor¬ 
mance and cost. Additional considerations include third party certification to NSF/ANSI stan¬ 
dards, appropriate mechanical warning devices, and ease of serviceability. 

8.1 Treatment Alternatives 

The technologies that are most amenable to POU treatment include column adsorption with AA, 
IBS, or RO with pre-filtration. The decision trees in Section 3 lead to the most appropriate POU 
technology among these choices. 

8.1.1 Adsorption Point-of-Use Treatment 

While finished water pH values will likely be much higher than the optimal pH for activated 
alumina (pH 6.0), it can be operated on a disposable basis at higher pH values. Modified 
AA and IBS provide improved treatment capacity across a broader pH range, and may be 
preferred depending upon the cartridge replacement frequency selected by the system. Col¬ 
umn operation has the advantages of simple operation, low maintenance, low relative cost, 
small under-the-counter footprint, and high treatment capacity. Additionally, the break- 


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117 




through kinetics of sorption technologies are slow and more readily detected by routine 
monitoring. 

Figure 8-1 shows how POU adsorption equipment is typically connected to kitchen plumb¬ 
ing. 



Figure 8-1. Point-Of-Use Adsorption Setup (Kinetico). 

Adsorption columns are typically operated to a set volume to prevent arsenic leakage. This 
is accomplished through the use of a metered cartridge that provides flow totalization and 
will automatically shut-off water flow once the unit reaches the prescribed volume limit. 
Figure 8-2 shows a cross-section of one manufacturer’s adsorption cartridge. 


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Feed Water 


Turbine 


Inlet 


Gearing 


Measured 

Shut-off 

Assembly 


Filter 



Filtered Water 
Outlet 

Flow Control 


Filter 


Arsenic 

Media 


Figure 8-2. Metered Automatic Cartridge (Kinetico). 

8.1.2 Reverse Osmosis Point-of-Use Treatment 

RO POU devices are recommended for treating arsenic-rich water containing high levels of 
sulfates, phosphates, or total dissolved solids. When operating at typical tap pressures, RO 
devices commonly achieve greater than 95% As(V) rejection at a water recovery of 10- 
25%. Most units are designed with pre- and post-filters. Pre-filtration through granular 
media is applied to reduce solids loading and extend membrane life. For chlorine sensitive 
membranes, pre-filtration typically utilizes a dechlorinating media such as granular acti¬ 
vated carbon. Post-filtration utilizes carbon or arsenic adsorbent media and serves as a final 
guard step. 


Although the cost of RO POU devices is relatively high compared to other possible options, 
the immediate improvement of the overall water quality could make it very attractive to 
customers. The potential disadvantages associated with RO systems include poor water 
recovery, disposal of the reject stream, and high capital cost. 


The most common types of membranes used for RO applications are cellulose acetate, thin- 
film polyamide composites, and sulfonated polysulfone. The membranes are manufactured 
in various forms, including tubes, sheets, and hollow fibers. The membrane is then con¬ 
structed into a cartridge called an RO module, either spiral wound or hollow fiber. 


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Most RO POU devices operate at tap water pressure, and therefore have relatively poor 
water recoveries. Permeate is sent to a bladder tank large enough to meet on-demand re¬ 
quirements. Typical production rates range from 5-15 gpd. 

Over time, the membrane surface will require cleaning in order to maintain performance. 
This capability is built in to most RO devices. Depending on the specific design, the water 
source for washing the membrane surface may either be feed water or permeate. 

Figure 8-3 shows how RO POU equipment is typically connected to kitchen plumbing. 


HOUSEHOLD 
WATER IN 




Figure 8-3. Point-Of-Use Reverse Osmosis Setup (Kinetico). 


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8.2 Implementation Considerations 


Amendments to the SDWA in 1996 explicitly allow utilities to install POU treatment devices to 
achieve compliance with the NPDWRs. More information on the implementation of a POU pro¬ 
gram can be found in the USEPA’s Guidance for Implementing a Point-of-Use or Point-oj-Entry 
Treatment Strategy for Compliance with the Safe Drinking Water Act (USEPA, 2002b Draft). 

The implementation of a centrally managed POU program is very different from application of 
centralized treatment. In many cases, the customer’s acceptance of the treatment unit is affected by 
familiarity with the technology, the need for treatment, the appearance of the unit, and other subjec¬ 
tive factors. Many homeowners currently employ some form of POU treatment such as carbon 
filtration or water softening. These products are generally used to enhance aesthetic properties of 
water, and are therefore used voluntarily. Under a centrally managed POU treatment program, all 
customers would be required to employ treatment devices in their home. As such, utility staff or 
contractors would need access inside individual homes to install treatment devices, make plumbing 
modifications, and make periodic O&M checks. The extent of customer acceptance and potential 
for resistance associated with this utility-customer interface are not well known. 

8.2.1 Program Oversight 

POU units must be owned, controlled, and maintained by the public water system or 
by a contractor hired by the public water system to ensure proper operation and main¬ 
tenance of the device and compliance with MCLs. The utility must retain oversight of 
unit installation, maintenance, and sampling. While this provision does not require the 
utility to perform all maintenance or management functions - utilities are free to contract 
out these tasks - it does imply that the utility retains final responsibility of the quality and 
quantity of the water provided to the service community and must closely monitor all con¬ 
tractors. Further, the utility may not delegate its responsibility for the operation and main¬ 
tenance of POU devices installed as part of a compliance strategy to homeowners. 

The implications of this requirement to the utility are significant. The utility must decide 
whether it wants to implement the POU program in-house or contract out the necessary 
services. In one case, the utility would be the main contact with the customer, and utility 
staff would be responsible for installation, monitoring, record-keeping, and O&M activi¬ 
ties. This raises several important issues. First, many small utilities often have difficulty 
finding the time and budget to hire, train, and retain operators. Second, utilities that elect to 
keep the work in-house must provide staff training on installation and O&M procedures. 
Third, the utility should consider the liability implications of entering individuals’ homes to 
conduct work. If the utility decides to contract out the services, the vendor would be the 
main contact with the customer and the utility would need to monitor the contractor. 


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8.2.2 Cost 


There are a number of cost elements involved in conducting a POU program. These in¬ 
clude: 

• Capital cost of POU devices. The typical cost ranges of RO devices and adsorption 
units are $300-$ 1,000 and $100-$300 each, respectively. 

• Installation labor. Installation of each device is anticipated to take 30 to 60 minutes 
assuming no significant plumbing modifications are necessary. 

• Installation parts 

• Replacement parts. Carbon-based pre-filters typically cost between $15-50. New mem¬ 
branes typically cost about $ 150. 

• Water quality analyses. Arsenic can be measured by a commercial laboratory for ap¬ 
proximately $10-$20 per sample. 

• O&M labor. 

8.2.3 Compliance Monitoring 

The current approach is that compliance monitoring would be conducted for each and every 
installed POU device, though only one-third within the same year. A representative moni¬ 
toring approach that requires less frequency monitoring is under evaluation. States may 
have more stringent monitoring requirements. Samples can be taken by the utility or the 
contractor. 

8.2.4 Mechanical Warnings 

Each POU treatment device installed as part of a compliance strategy must be equipped 
with a warning device (e.g., alarm, light, etc.) that will alert users when their unit is no 
longer adequately treating their water. Alternatively, units may be equipped with an auto¬ 
matic shut-off mechanism to meet this requirement. Several communities have implemented 
POU treatment strategies using units equipped with water meters and automatic shut-off 
devices to disable the units after a specified amount of water has been treated to prevent 
contaminant breakthrough. 

8.2.5 Operations and Maintenance 

Periodic maintenance is necessary to ensure that the devices are functioning properly and 
producing tap water in compliance with the arsenic MCL. O&M activities consist of both 
regular scheduled tasks as well as emergency troubleshooting responses. 

The sorbent media or RO membrane should be replaced periodically either on a set fre¬ 
quency or based on monitoring and tracking use. Both replacement schedules should be 
based on pilot testing results. The Arsenic Rule also stipulates that the POU device be 
equipped with mechanical warnings to ensure that customers are automatically notified of 
operational problems. Many devices include a programmable indicator that tracks cumula¬ 
tive water use, and serves as a convenient visual guide for the remaining life of the POU 


Arsenic Treatment Technology> Evaluation Handbook for Small Systems 


122 



device. However, it is not recommended that the utility depend solely on the customer for 
POU servicing. Rather, there should be an established schedule that is made public to the 
community and adhered to. 

8.2.6 Customer Education and Residential Access 

Utilities should attempt to educate the public prior to implementing a POU strategy. This 
education may include public hearings, water bill inserts, posters, or notices in print or on 
radio or TV. When presented with the facts, most people will happily provide the water 
utility with access to ensure their ongoing effectiveness. 

To address the possibility that an individual or a group of individuals may refuse to provide 
utility personnel with the necessary access, the utility may need to convince the local gov¬ 
ernment to pass an ordinance guaranteeing water utility personnel access to service treat¬ 
ment units. To meet the legal responsibility to provide water in compliance with all NPDWRs, 
the utility may also have to pass an ordinance that requires customers to use POU treatment 
units, and that provides the utility with the authority to shut off a customer’s water if the 
customer refuses to allow installation and maintenance of, tampers with, bypasses, or re¬ 
moves the treatment unit. 

To minimize the burden associated with gaining access to individual residences, POU sam¬ 
pling should be coordinated with routine maintenance. Reducing the number of house 
visits will reduce administrative costs and travel time, resulting in substantial cost savings 
as well reducing the disruption to the residents. 

8.2.7 Residual Oxidant in Distribution System 

In order to effectively use many sorbent type POU devices, the arsenic must be in its As(V) 
form as it is treated at the tap. RO type POU devices may also work more efficiently if 
arsenic is oxidized. This may require installation of a POU oxidation unit or centralized 
oxidation. If anoxic conditions occur in the distribution system, there is a potential for 
arsenic to reduce back to the As(III) state. This would drastically decrease the effectiveness 
of most of the sorptive type POU devices. Therefore, maintaining an adequate residual 
oxidant in the distribution system is important. 

8.2.8 Waste Handling 

The type of waste produced from a POU device will depend on the treatment employed. 
RO treatment will produce a continuous liquid waste stream (i.e., retentate) that should be 
suitable for disposal in an on-site or community sewerage system (see Section 2.4). Con¬ 
versely, with column adsorption treatment, the only waste is exhausted media, which is 
produced on a periodic basis. 

Because the solid residuals generated by POU units are collected from individual house¬ 
holds, these wastes may be exempt from federal regulation as hazardous wastes, regardless 
of their toxicity. However, state regulations and each state’s implementation of federal 
regulation can vary. In the case of liquid wastes, local wastewater treatment plants may 


Arsenic Treatment Technology Evaluation Handbook for Small Systems 


123 



issue their own limits for the disposal of arsenic. It is anticipated that this waste will not 
exceed the TC characteristics and will be disposable in a municipal landfill. Additionally, 
POU manufacturers or vendors may also provide waste disposal services for the POU de¬ 
vices. 

8.3 Device Certification 

To meet the requirements of the SDWA, POU devices installed as part of a compliance strategy 
must be certified according the American National Standards Institute (ANSI) standards, if a stan¬ 
dard exists for that type if device. RO POU devices must be certified as per ANSI/NSF 58 (2002) 
- Reverse Osmosis Drinking Water Treatment Systems. POU devices utilizing a sorption technol¬ 
ogy such as AA or an IBS must be certified as per ANSI/NSF 53 (2002) - Drinking Water Treatment 
Units - Health Effects. 


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Section 9 
References 


AwwaRF (2000). Arsenic Treatability Options and Evaluation of Residuals Management Issues, 
Amy, G.L., M. Edwards, P. Brandhuber, L. McNeill, M. Benjamin, F. Vagliasindi, K. 
Carlson, and J. Chwirka. Awwa Research Foundation, Denver, CO. 

AwwaRF (2002). Implementation of Arsenic Treatment Systems - Part 1. Process Selection, 

Chowdhury, Z., S. Kommineni, R. Narasimhan, J. Brereton, G. Amy, and S. Sinha. Awwa 
Research Foundation, Denver, CO. 

Clifford, Dennis (1999). Presentation at Arsenic Technical Work Group. Washington, D.C. 

Clifford, Dennis (2001). Arsenic Treatment Technology Demonstration Drinking Water 

Assistance Program for Small Systems, Final Report to the Montana Water Resources 
Center, March 2001. 

Fields, Keith, Abraham Chen, and Lili Wang (2000a). Arsenic Removal from Drinking Water by 
Coagulation/Filtration and Lime Softening Plants, EPA 600R00063, Prepared by Battelle 
under contract 68C70008 for U.S. EPA ORD, June 2000. 

Fields, Keith, Abraham Chen, and Lili Wang (2000b). Arsenic Removal from Drinking Water by 
Iron Removal Plants, EPA 600R00086, Prepared by Battelle under contract 68C70008 for 
U.S. EPA ORD, August 2000. 

Ghurye, Ganesh and Dennis Clifford (2001). Laboratory Study on the Oxidation of As (III) to 
As(V), EPA 600R01021, Prepared under contract 8CR311-NAEX for EPA ORD, March 
2001. 

Hanson, Adrian, Jared Bates, Dean Heil, Andrew Bistol (1999). Arsenic Removal from Water 
Using Greensand: Laboratory Scale Batch and Column Tests. New Mexico State 
University, Las Cruces, NM, June 1999. 

Kempic, Jeffery (2002), Teleconference on October 29, 2002. 

MacPhee, Michael J., Gail E. Charles, and David A Cornwell (2001). Treatment of Arsenic 
Residuals from Drinking Water Removal Processes, EPA 600R 01033, Prepared by 
Environmental Engineering & Technology, Inc. under contract 8CR613-NTSA for EPA 
ORD, June 2001. 

National Research Council (NRC) (1999). Arsenic in Drinking Water. National Academy Press, 
Washington, D.C. 


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NSF International (2001a). Environmental Technology Verification Report: Removal of Arsenic 
in Drinking Water - Hydranautics ESPA2-4040 Reverse Osmosis Membrane Element 
Module, NSF 0120EPADW395, March 2001. 

NSF International (2001b). Environmental Technology Verification Report: Removal of Arsenic 
in Drinking Water - KOCH Membrane Systems TFC - ULP4 Reverse Osmosis 
Membrane Module, NSF 0125EPADW395, August 2001. 

Rubel, Frederick, Jr. Design Manual - Removal of Arsenic from Drinking Water Supplies by Ion 
Exchange, EPA DRAFT. 

Rubel, Frederick, Jr. Design Manual - Removal of Arsenic from Drinking Water Supplies by 
Adsorptive Media, EPA 600-R-03-019, 2003. 

Selvin N., Messham G., Simms J., Pearson I., and Hall J. (2000). The Development of Granular 
Ferric Media - Arsenic Removal and Additional Uses in Water Treatment. Proceedings of 
the AWWA Water Quality Technology Conference, Salt Lake City. 

Tumalo, Jamie (2002). U.S. Filter. Personal Conversation with Andrew Hill. 

United States Environmental Protection Agency (1998). Variance Technology Findings for 
Contaminants Regulated Before 1996, EPA 815R98003, September 1998. 

United States Environmental Protection Agency (2000). Technologies and Costs for Removal of 
Arsenic from Drinking Water, EPA 815R00028, Prepared by Malcolm Pimie, Inc. under 
contract 68C60039 for EPA ORD, December 2000. 

United States Environmental Protection Agency (2001). Federal Register, Final Arsenic Rule, 

40 CFR Parts 9, 141, and 142. 

United States Environmental Protection Agency (2002a). Implementation Guidance for the 

Arsenic Rule - Drinking Water Regulations for Arsenic and Clarifications to Compliance 
and New Source Contaminants Monitoring, EPA 816K02018, August 2002. 

United States Environmental Protection Agency (2002b Draft). Guidance on Implementing a 
Point-of-Use or Point-of Entry Treatment Strategy for Compliance with the Safe 
Drinking Water Act, EPA xxxx02xxx DRAFT, March 2002. 

Wang, Lili, Abraham Chen, and Keith Fields (2000). Arsenic Removal from Drinking Water by 
Ion Exchange and Activated Alumina Plants, EPA 600R00088, Prepared by Battelle 
under contract 68C70008 for U.S. EPA ORD, October 2000. 


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Disclaimer 


The information in this document has been subjected to the Agency’s peer and administrative re¬ 
views and has been approved for publication as an EPA document. Mention of trade names or 
commercial products does not constitute an endorsement or recommendation of use. 



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